Tumor islands in resected early-stage lung adenocarcinomas are associated with unique clinicopathologic and molecular characteristics and worse prognosis

The role of spread through air spaces (STAS) in lung adenocarcinoma prognosis and therapeutic decision making

Spread through air spaces (STAS) was included as a novel pattern of invasion in lung adenocarcinoma by the World Health Organization in 2015. Since then, multiple studies have investigated the association of STAS with clinicopathological and molecular features and its implication in the prognosis of early stage lung cancer patients undergoing different surgery types. The aim of this comprehensive review is to present current data on the role of STAS and its perspective in lung adenocarcinoma management.

Spread through air spaces affects survival and recurrence of patients with clinical stage IA non-small cell lung cancer after wedge resection

Background

Spread through air spaces (STAS) is reportedly a significant risk factor for recurrence and a prognostic factor in patients with non-small cell lung cancer (NSCLC), especially after sublobar resection. Because wedge resection (WR) is associated with insufficient margins, we hypothesized that STAS has a greater prognostic impact in patients who undergo WR compared with segmentectomy. We aimed to clarify the value of STAS as a prognostic factor in patients with NSCLC after WR.

Methods

We evaluated 217 patients with clinical stage IA NSCLC who underwent sublobar resection. The prognostic impact of STAS in these patients was compared between the WR (n=100) and segmentectomy (n=117) cases.

Results

STAS was present in 15.7% of the 217 patients. STAS was a significant prognostic factor for overall survival in univariate (P<0.001) and multivariate (P=0.003) analyses for the WR cases, but not the segmentectomy cases (P=0.399). STAS was also a significant prognostic factor for freedom from recurrence in univariate (P=0.010) and multivariate (P=0.024) analyses for the WR cases, but was only marginally significant for the segmentectomy cases (P=0.050, univariate analysis). The solid tumor size on chest computed tomography was significantly related to STAS. A cut-off solid tumor size of 1.7 cm for predicting the presence of STAS was determined by receiver operating characteristic analysis.

Conclusions

STAS was a significant prognostic factor for patients with clinical stage IA NSCLC who underwent WR, but not those who underwent segmentectomy.

Spread Through Air Spaces (STAS) in Lung Cancer: A Multiple-Perspective and Update Review

BACKGROUND

Spread through air spaces (STAS) is a spreading phenomenon of lung cancers, which is defined as tumor cells within air spaces in the lung parenchyma beyond the edge of the main tumor. To date, several articles have reviewed the studies concerning the significance of STAS; however, most articles focused on the prognosis without summarizing the significance of STAS on other aspects. In this review, we comprehensively summarized the current literature related to STAS, so as to explore the clinical significance of STAS from multiple perspectives.

MAIN BODY

This section provided a comprehensive overview of the significance of STAS from multiple perspectives and summarized current controversies and challenges in the diagnosis and clinical application.

CONCLUSION

STAS is a conspicuous spreading phenomenon of lung cancers indicating worse prognosis; nevertheless, the treatment strategy for patients with STAS remains to be discussed. Further studies are needed to elaborate whether a STAS-positive patient who underwent limited resection needs a second operation or postoperative adjuvant treatment. Meanwhile, the internal mechanism of STAS formation is largely undiscovered. Whether the capability of detachment-migration-reattachment in STAS tumor cells is achieved at the time of primary tumorigenesis or in the progress of tumor development needs to be studied, and the related signal pathways or genetic alterations need to be explored. With this information, it may be possible to improve the prognosis of patients with STAS-positive lung cancers.

Three-Dimensional Histologic, Immunohistochemical, and Multiplex Immunofluorescence Analyses of Dynamic Vessel Co-Option of Spread Through Air Spaces in Lung Adenocarcinoma

INTRODUCTION

Spread through air spaces (STAS) is a method of invasion in lung adenocarcinoma and is associated with tumor recurrence and poor survival. The spatial orientation of STAS cells in the lung alveolar parenchyma is not known. The aim of this study was to use high-resolution and high-quality three-dimensional (3D) reconstruction of images from immunohistochemical (IHC) and multiplex immunofluorescence (IF) experiments to understand the spatial architecture of tumor cell clusters by STAS in the lung parenchyma.

METHODS

Four lung adenocarcinomas, three micropapillary-predominant and one solid predominant adenocarcinoma subtypes, were investigated. A 3D reconstruction image was created from formalin-fixed, paraffin-embedded blocks. A total of 350 serial sections were obtained and subjected to hematoxylin and eosin (100 slides), IHC (200 slides), and multiplex IF staining (50 slides) with the following antibodies: cluster of differentiation 31, collagen type IV, thyroid transcription factor-1, and E-cadherin. Whole slide images were reconstructed into 3D images for evaluation.

RESULTS

Serial 3D image analysis by hematoxylin and eosin, IHC, and IF staining revealed that the micropapillary clusters and solid nests of STAS are focally attached to the alveolar walls, away from the main tumor.

CONCLUSIONS

Our 3D reconstructions found that STAS tumor cells can attach to the alveolar walls rather than appearing free floating, as seen on the two-dimensional sections. This suggests that the tumor cells detach from the main tumor, migrate through air spaces, and reattach to the alveolar walls through vessel co-option, allowing them to survive and grow. This may explain the higher recurrence rate and worse survival of patients with STAS-positive tumors who undergo limited resection than those who undergo lobectomy.

CT-based radiomics and machine learning to predict spread through air space in lung adenocarcinoma

PURPOSE

Spread through air space (STAS) is a novel invasive pattern of lung adenocarcinoma and is also a risk factor for recurrence and worse prognosis of lung adenocarcinoma. The aims of this study are to develop and validate a computed tomography (CT)‑based radiomics model for preoperative prediction of STAS in lung adenocarcinoma.

METHODS AND MATERIALS

This retrospective study was approved by an institutional review board and included 462 (mean age, 58.06 years) patients with pathologically confirmed lung adenocarcinoma. STAS was identified in 90 patients (19.5%). Two experienced radiologists segmented and extracted radiomics features on preoperative thin-slice CT images with radiomics extension independently. Intraclass correlation coefficients (ICC) and Pearson's correlation were used to rule out those low reliable (ICC < 0.75) and redundant (r > 0.9) features. Univariate logistic regression was applied to select radiomics features which were associated with STAS. A radiomics-based machine learning predictive model using a random forest (RF) was developed and calibrated with fivefold cross-validation. The diagnostic performance of the model was measured by the area under the curve (AUC) of receiver operating characteristic (ROC).

RESULTS

With univariate analysis, 12 radiomics features and age were found to be associated with STAS significantly. The RF model achieved an AUC of 0.754 (a sensitivity of 0.880 and a specificity of 0.588) for predicting STAS.

CONCLUSION

CT-based radiomics model can preoperatively predict STAS in lung adenocarcinoma with good diagnosis performance.

KEY POINTS

• CT-based radiomics and machine learning model can predict spread through air space (STAS) in lung adenocarcinoma with high accuracy. • The random forest (RF) model achieved an AUC of 0.754 (a sensitivity of 0.880 and a specificity of 0.588) for predicting STAS.

Stepwise flowchart for decision making on sublobar resection through the estimation of spread through air space in early stage lung cancer1

OBJECTIVES

The sensitivity for tumor spread through air space (STAS), an independent risk factor for locoregional recurrence after sublobar resection for lung cancer, has been relatively low in frozen sections. We aimed to determine predictors with high negative predictive value for the presence of STAS and to provide the flowchart in combination with these predictors for the decision-making for sublobar resection.

MATERIALS AND METHODS

Between July 2015 and December 2017, 387 patients who underwent surgery for non-small cell lung cancer (NSCLC) with pathologic findings of the total masses measuring ≤ 2 cm were enrolled. The lesions were divided into two groups according to presence of STAS. We compared the preoperative characteristics, operative data, and developed a flowchart for STAS prediction using receiver operator characteristic curve analysis and multivariable logistic regression.

RESULTS

The STAS-positive group (N = 111) had a significantly higher preoperative tumor size (1.70 [1.5] vs 1.50 [0.69], p < 0.001) and standardized uptake value tumor-to-liver (SUV T/L) ratio (1.40 [1.60] vs 0.60 [1.10], p < 0.001) and a significantly lower two-dimensional ground-glass opacity (GGO) percentage (35.86 [61.00] vs 78.14 [39.00], p < 0.001). Meanwhile, the STAS-negative group (N = 286) had higher lepidic predominance (41.6% vs. 1.8%, p < 0.001). We developed a flowchart for predicting STAS in combination with two-dimensional GGO percentage on computed tomography (CT), SUV T/L ratio on positron-emission CT, and lepidic predominant pattern. The sensitivity, specificity, and negative predictive value for STAS positivity were 79.3%, 68.5%, and 89.5%, respectively.

CONCLUSIONS

The stepwise flowchart using two-dimensional GGO percentage on CT, maximum SUV, and lepidic predominance might be helpful in selecting patients with early NSCLC for sublobar resection.

Spread through air spaces is an independent predictor of recurrence in stage III (N2) lung adenocarcinoma

OBJECTIVES

Spread through air space (STAS) is recognized as a pattern of invasion in lung adenocarcinoma and has been reported to be a predictor of recurrence and survival in patients with early-stage lung adenocarcinoma. However, this parameter has not been studied well in stage III (N2) lung adenocarcinoma. In this study, we evaluated the association between STAS invasion patterns and recurrence and survival in stage III (N2) lung adenocarcinoma.

METHODS

We retrospectively reviewed data from 76 patients at University of Tokyo with stage III (N2) lung adenocarcinoma who underwent surgery from August 1998 to December 2013. Statistical analysis was performed to determine the impact of STAS invasion clinicopathological features and clarify the relationship between this pattern of invasion and survival.

RESULTS

Tumour STAS was observed in 46 of 76 patients (60.5%) and was significantly associated with the presence of lymphatic invasion (P < 0.001), papillary components (P < 0.001) and micropapillary components (P < 0.001). STAS was also significantly associated with recurrence (5-year recurrence-free probability: 19.0% vs 46.1%, P < 0.05). Univariate analyses showed that STAS was a significant risk factor for recurrence (hazard ratio 1.94, 95% confidence interval 1.07-3.51; P = 0.029).

CONCLUSIONS

The presence of STAS invasion pattern is a significant risk factor for recurrence in stage III (N2) lung adenocarcinoma.

Tumor Spread Through Air Spaces Is a Predictor of Occult Lymph Node Metastasis in Clinical Stage IA Lung Adenocarcinoma

INTRODUCTION

In patients with stage IA lung adenocarcinoma (ADC), sublobar resection and tumor spread through air spaces (STAS) are associated with high rates of locoregional recurrence, half of which occur within the regional lymph nodes (LNs). Our objectives were to investigate the association between occult LN metastasis (ONM) and STAS and to assess their prognostic value in patients with clinical stage IA lung ADC.

METHODS

The association between STAS and ONM was analyzed in patients who underwent lobectomy and LN dissection for clinical stage IA lung ADC (n = 809). Multivariable logistic regression analysis was carried out to identify predictors of ONM. Site-specific recurrence by surgical procedure was investigated in patients with pathologic node-negative disease (n = 1055) using a competing risk approach.

RESULTS

ONM was identified in 129 patients (16%)-one-third of ONMs were located only in intrapulmonary nodes. STAS was more common in patients with ONM than in those without ONM (67% versus 39%; p < 0.001) and in patients with multiple ONMs than in those with a single ONM (86%-89% versus 60%-67%). STAS was a significant predictor of ONM (p = 0.004) on multivariable analysis, independent of tumor size, maximum standardized uptake value, and lymphovascular invasion. In patients with STAS-positive ADC (high ONM risk), the risk of recurrence in the treated lobe and regional LNs increased as the extent of resection decreased (recurrence risk: lobectomy < segmentectomy < wedge resection). In patients with STAS-negative ADC, the risk of locoregional recurrence did not differ by procedure type.

CONCLUSIONS

Presence of STAS predicts ONM in patients with clinical stage IA lung ADC and can help stratify risk of recurrence by extent and type of resection.

Advances In Research Of Spreading Through Air Spaces And The Effects On The Prognosis Of Lung Cancer

The concept of spread through air spaces (STAS) has been described as a new form of invasion in the lung in the 2015 WHO classification of Lung Tumors, namely invasion through alveolar spaces. STAS is a prognostic factor independent of growth pattern and tumor stage, and it is also an independent risk factor for unfavorable prognosis of stage I lung adenocarcinoma (ADC) and stage I lung squamous cell carcinoma (SCC). The pathological characteristics are different between ADC and SCC. STAS is not reported as routine, so setting a unified pathological reading standard, and hunting for STAS as a regular reading process is urgently advocated. We write this review to investigate the research progress of STAS and its effects on the prognosis of lung cancer.

KRAS Mutations Predict Response and Outcome in Advanced Lung Adenocarcinoma Patients Receiving First-Line Bevacizumab and Platinum-Based Chemotherapy

Bevacizumab, combined with platinum-based chemotherapy, has been widely used in the treatment of advanced-stage lung adenocarcinoma (LADC). Although KRAS (V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog) mutation is the most common genetic alteration in human LADC and its role in promoting angiogenesis has been well established, its prognostic and predictive role in the above setting remains unclear. The association between KRAS exon 2 mutational status and clinicopathological variables including progression-free survival and overall survival (PFS and OS, respectively) was retrospectively analyzed in 501 Caucasian stage IIIB-IV LADC patients receiving first-line platinum-based chemotherapy (CHT) with or without bevacizumab (BEV). EGFR (epidermal growth factor receptor)-mutant cases were excluded. Of 247 BEV/CHT and 254 CHT patients, 95 (38.5%) and 75 (29.5%) had mutations in KRAS, respectively. KRAS mutation was associated with smoking (p = 0.008) and female gender (p = 0.002) in the BEV/CHT group. We found no difference in OS between patients with KRAS-mutant versus KRAS wild-type tumors in the CHT-alone group (p = 0.6771). Notably, patients with KRAS-mutant tumors demonstrated significantly shorter PFS (p = 0.0255) and OS (p = 0.0186) in response to BEV/CHT compared to KRAS wild-type patients. KRAS mutation was an independent predictor of shorter PFS (hazard ratio, 0.597; p = 0.011) and OS (hazard ratio, 0.645; p = 0.012) in the BEV/CHT group. G12D KRAS-mutant patients receiving BEV/CHT showed significantly shorter PFS (3.7 months versus 8.27 months in the G12/13x group; p = 0.0032) and OS (7.2 months versus 16.1 months in the G12/13x group; p = 0.0144). In this single-center, retrospective study, KRAS-mutant LADC patients receiving BEV/CHT treatment exhibited inferior PFS and OS compared to those with KRAS wild-type advanced LADC. G12D mutations may define a subset of KRAS-mutant LADC patients unsuitable for antiangiogenic therapy with BEV.

[Progress on the Study of Tumor Spread Through Air Spaces in the Clinicopathological Characteristics of Lung Adenocarcinoma and Its Influence on the Surgical Treatment and Prognosis of Lung Cancer]

肿瘤肺泡腔内播散（tumor spread through air spaces, STAS）作为一种新的病理侵袭方式，与诸多临床病理因素紧密相关。在肺腺癌中，微乳头和实体型病理亚型与之关系最为密切；针对早期肺腺癌存在STAS，手术类型的治疗上肺叶切除似乎优于亚肺叶切除而获益，可能上调早期肺癌的病理分期；同时，STAS与鳞癌等非小细胞肺癌（non-small cell lung cancer, NSCLC）关系密切。此外，STAS的术中冰冻切片病理检测困难，亦有争议存在。STAS作为肿瘤复发的独立危险因素，亦是提示预后不良的重要因素，本文将STAS的研究现状和进展作一综述。

Tumor Spread Through Air Spaces Is a Survival Predictor in Non-Small-Cell Lung Cancer

BACKGROUND

Tumor spread through air spaces (STAS) is a newly recognized invasion pattern in non-small-cell lung cancer (NSCLC). However, the clinical application value of STAS in NSCLC remains to be clarified. We aimed to comprehensively explore the potential role of STAS as a prognostic indicator in NSCLC.

PATIENTS AND METHODS

A systematic search was performed in PubMed, Embase, Cochrane Library, and Web of Science until April 15, 2018. A quantitative meta-analysis was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

RESULTS

A total of 3231 patients from 8 studies were included. STAS was observed in 1204 cases (37.3%). A significant association was found between STAS and poor progression-free survival (PFS) (hazard ratio [HR], 1.789; P < .001) and overall survival (OS; HR, 1.488; P < .001). STAS was also an independent prognostic factor for PFS (HR, 1.632; P < .001) and OS (HR, 1.475; P < .001) without obvious heterogeneity. Subgroup analyses and meta-regression showed histology type, tumor, node, metastases (TNM) stage, publication year, sample size, region, and quality score did not alter prognostic value of STAS. Tumor STAS was associated with male sex (P < .001), history of smoking (P < .001), tumor budding (P = .038), vascular invasion (P < .001), lymphatic invasion (P < .001), pleural invasion (P < .001), T stage (P < .001), N stage (P < .001), and TNM stage (P < .001). The publication bias was observed. After adjustment using a nonparametric "trim-and-fill" method, corrected HRs had no significant change.

CONCLUSION

Tumor STAS is associated with clinicopathologically aggressive features and could be exploited as a novel prognostic predictor in NSCLC.

Tumor Spread Through Air Spaces in Non-Small Cell Lung Cancer: A Systematic Review and Meta-Analysis

BACKGROUND

A series of studies have assessed the clinicopathological features and prognostic impact of spread through air spaces (STAS) in non-small cell lung cancer (NSCLC) bringing conflicting findings so far. We performed a systematic review and meta-analysis to synthesize the available evidence regarding to the prognostic value of STAS in NSCLCs.

METHODS

Studies were identified by searching databases including PubMed, EMBASE, Web of Science, and Cochrane Library up to August 2018 without language restrictions. Results of these searches were filtered according to a set of eligibility criteria and analyzed in line with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines.

RESULTS

A total of 3,754 patients from 14 studies were selected for the present study. The pooled results suggested that presence of STAS was associated with worse recurrence-free survival (hazard ratio [HR], 1.975; 95% confidence interval [CI], 1.691 to 2.307; p < 0.001) and overall survival (HR, 1.75; 95% CI, 1.375 to 2.227; p < 0.001) in NSCLCs. Subgroup analysis by histology type indicated the presence of STAS was significantly associated with inferior recurrence-free survival in resected lung adenocarcinoma (n = 7; HR, 2.288; 95% CI, 1.843 to 2.840; I² = 7.80%), lung squamous cell carcinoma (n = 3; HR, 1.622; 95% CI, 1.279 to 2.056; I² = 0%), and lung pleomorphic carcinoma (n = 1; HR, 4.76; 95% CI, 1.168 to 19.398). Additionally, a number of clinicopathological characteristics indicating STAS in NSCLCs are summarized.

CONCLUSIONS

Our study indicates that tumor STAS was a potentially significant prognostic predictor for surgical patients with NSCLCs. The prognostic impact of STAS present in the resection margin remains undetermined. Further large-scale prospective studies are warranted to confirm the prognostic significance of STAS in patients with NSCLCs.

Predictive value of a prognostic model based on pathologic features in lung invasive adenocarcinoma

OBJECTIVES

Tumor spread through air spaces (STAS) was recently reported as a novel risk factor for the prognosis of patients with resected lung adenocarcinoma that indicates invasive tumor behavior. The purpose of this study was to build a prognostic model consisting of STAS and other pathologic features including visceral pleural invasion (VPI), vascular invasion (VI) and histological subtype (HS) in lung invasive adenocarcinoma.

MATERIALS AND METHODS

A total of 289 patients with resected lung invasive adenocarcinomas ≤4 cm were analyzed retrospectively to evaluate the potential prognostic value of STAS, VPI, VI and HS for recurrence-free survival (RFS) and overall survival (OS).

RESULTS

STAS was observed in 143 patients (49.5%). Univariate and multivariate analysis showed that STAS, VPI, VI and HS were significant prognostic factors for poorer RFS and OS. Thus, a prognostic model including STAS, VPI, VI and HS was built using the results of the multivariate analysis. Nomograms were developed to predict the 5-year RFS and OS. The concordance index (C-index) of the prognostic model was 0.8122 for predicting 5-year RFS and 0.8539 for predicting 5-year OS in the internal validation. Moreover, the calibration curves for the 5-year RFS and OS showed that the nomograms were calibrated well. In addition, a similar predicted capability of the prognostic model was observed in the validation cohort.

CONCLUSION

STAS, VPI, VI and HS were significant prognostic factors for poorer RFS and OS. The prognostic model including STAS, VPI, VI and HS could effectively predict prognosis.

CT Manifestations of Tumor Spread Through Airspaces in Pulmonary Adenocarcinomas Presenting as Subsolid Nodules

PURPOSE

The aim of this study was to identify potential computed tomography manifestations of pulmonary adenocarcinomas presenting as subsolid nodules and associated with the histologic evidence of spread of tumor through air spaces (STAS).

MATERIALS AND METHODS

From a radiologic-pathologic repository of resected pulmonary adenocarcinomas including 203 subsolid nodules, 40 STAS-positive nodules were randomly selected and matched to 40 STAS-negative nodules. Total average diameter, as well as average and long-axis diameters of the solid component, was measured. The proportion of solid component diameter to total average diameter was calculated. Measurements and proportions between STAS-positive and STAS-negative nodules were compared with paired samples t test, χ test, or the Fisher exact test.

RESULTS

The total average diameter in STAS-positive nodules was significantly larger than in STAS-negative nodules (P=0.024). The average and long-axis diameters of the solid component of STAS-positive nodules were significantly larger than that of STAS-negative nodules (P=0.001 and 0.003). The proportion of solid component to total average diameter was significantly larger in STAS-positive than in STAS-negative nodules (P=0.041). At a threshold of ≥10 mm for the average and the solid component long-axis diameters, significantly more nodules were STAS-positive than STAS-negative (P=0.015 and 0.001).

CONCLUSIONS

Total average diameter, average and long-axis diameters of the solid component, and a high proportion of solid component diameter compared with total average diameter are computed tomography manifestations of subsolid pulmonary adenocarcinomas with STAS. These findings could serve as an in-vivo tool for the likelihood estimation of STAS, and consequently influence management of subsolid adenocarcinomas.

Relationship between stromal cells and tumor spread through air spaces in lung adenocarcinoma

Background

The mechanism underlying tumor spread through air spaces (STAS) has not been well studied. We investigated the role of tumor stromal cells in the pathogenesis of STAS from a pathological perspective and evaluated the prognostic significance of tumor stromal cells and STAS in postoperative patients with lung adenocarcinoma.

Methods

We retrospectively analyzed 208 postsurgical patients with stage I–IIIA lung adenocarcinoma. The presence of STAS was evaluated by hematoxylin and eosin staining. The expression of α‐smooth muscle actin (SMA)‐positive cancer‐associated fibroblasts (CAFs) and CD204‐positive tumor‐associated macrophages (TAMs) was analyzed by immunohistochemistry. A logistic regression model was applied to confirm the predictive factors of STAS. Survival analysis was performed to evaluate the effect of α‐SMA‐positive CAFs, CD204‐positive TAMs, and STAS on prognosis. A nomogram was generated to evaluate the prognosis of postoperative patients.

Results

Logistic regression suggested that the expression of α‐SMA‐positive CAFs (P < 0.001) and the number of CD204‐positive TAMs (P < 0.001) were related to the presence of STAS. The multivariate Cox proportional hazards model suggested that STAS (P = 0.004), α‐SMA‐positive CAFs (P < 0.001), and CD204‐positive TAMs (P < 0.001) were independent risk factors for prognosis. Harrell's c‐indexes for overall and recurrence‐free survival prediction based on nomograms were 0.84 (95% confidence interval 0.76–0.91) and 0.82 (95% confidence interval 0.76–0.89), respectively.

Conclusions

The presence of STAS was associated with high expression of α‐SMA and CD204 in lung adenocarcinoma. Nomograms including STAS and stromal cells as variables are recommended as practical models to evaluate the prognosis of lung adenocarcinoma patients.

Lobectomy Is Associated with Better Outcomes than Sublobar Resection in Spread through Air Spaces (STAS)-Positive T1 Lung Adenocarcinoma: A Propensity Score-Matched Analysis

INTRODUCTION

Spread through air spaces (STAS) is a form of invasion wherein tumor cells extend beyond the tumor edge within the lung parenchyma. In lung adenocarcinoma (ADC), we investigated the (1) association between STAS and procedure-specific outcomes (sublobar resection and lobectomy), (2) effect of surgical margin-to-tumor diameter ratio in STAS-positive patients, and (3) potential utility of frozen sections (FSs) for detecting STAS intraoperatively.

METHODS

We investigated 1497 patients who underwent lobectomy (n = 970) or sublobar resection (n = 527) for T1N0M0 lung ADC after propensity score matching. Outcomes were analyzed by using a competing risks approach. The effect of margin-to-tumor ratio on recurrence pattern (locoregional and distant) was investigated in patients who underwent sublobar resection. Five pathologists evaluated the feasibility of intraoperatively identifying STAS by using FSs (sensitivity, specificity, and interrater reliability).

RESULTS

On multivariable analysis after propensity score matching (349 pairs/procedure), sublobar resection was significantly associated with recurrence (subhazard ratio = 2.84 [p < 0.001]) and lung cancer-specific death (subhazard ratio = 2.63 [p = 0.021]) in patients with STAS but not in those without STAS. Patients with STAS who underwent sublobar resection had a higher risk of locoregional recurrence regardless of margin-to-tumor ratio (for a margin-to-tumor ratio of ≥1 versus <1, the 5-year cumulative incidence of recurrence rates were 16% and 25%, respectively); among patients without STAS, locoregional recurrences occurred in patients with margin-to-tumor ratio lower than 1 (a 5-year cumulative incidence of recurrence rate of 7%). The sensitivity and specificity for detecting STAS by use of FSs were 71% and 92%, with substantial interrater reliability (Gwet's AC1, 0.67).

CONCLUSIONS

In patients with T1 lung ADC with STAS, lobectomy was associated with better outcomes than sublobar resection was. Pathologists can recognize STAS on FSs.

Spread through air spaces in lung cancer patients is a risk factor for pulmonary metastasis after surgery

BACKGROUND

Spread through air spaces (STAS) is regarded as a significant risk factor for lung cancer recurrence. STAS consists of micropapillary clusters, solid nests, or single cells beyond the edge of the tumor into air spaces in the surrounding lung parenchyma. However, the patterns of lung cancer recurrence have not been clarified in patients with STAS. The aim of this study was to explore STAS and recurrence patterns in patients who underwent lung cancer surgery.

METHODS

Between January 2000 and December 2017, a total of 1,426 patients underwent complete resection of lung cancer. We studied 848 patients with pathological stage I disease who underwent surgery. Recurrence patterns and recurrence-free rates were determined from pathological findings, particularly the presence of STAS. Locoregional recurrences included surgical margin recurrences, hilar and mediastinal lymph node metastases, ipsilateral lobe metastases, and pleural dissemination, whereas distant recurrences included extrathoracic organ and contralateral lobe metastases.

RESULTS

STAS was observed in 139 of 848 (16.4%) cases. Recurrences developed in 108 (12.7%) cases: locoregional recurrences in 76 (9.0%), distant metastases in 27 (3.2%), and both in 5 (0.6%) cases. Among recurrences, pleural dissemination developed in 12 (1.4%) and pulmonary metastases in 46 (5.4%) cases. Five-year recurrence-free rates were 65.4% among patients with STAS and 89.0% among patients without STAS. Univariate and multivariate analyses revealed that STAS was a significant risk factor for recurrence (P<0.001), particularly locoregional recurrence (P=0.005). In addition, STAS was a significant risk factor for pulmonary metastasis (P=0.009).

CONCLUSIONS

Among pathological stage I patients who undergo complete resection of lung cancer, patients with STAS tend to develop locoregional recurrence and pulmonary metastases.

Correlation of tumor spread through air spaces and clinicopathological characteristics in surgically resected lung adenocarcinomas

OBJECTIVES

Tumor spread through air spaces (STAS) has recently been reported as a novel invasive pattern in lung adenocarcinoma, but the correlation between other clinicopathological and genetic profiles has not been well studied. The aim of this study was to investigate these correlations in patients with surgically resected lung adenocarcinoma.

MATERIALS AND METHODS

Five hundred consecutive patients with lung adenocarcinoma who underwent curative lung tumor resection and with available STAS profile were reviewed retrospectively from January to December 2016. The correlations of STAS presence and clinicopathological and genetic characteristics were analyzed.

RESULTS

One hundred thirty-four patients (26.8%) had positive STAS. The pathological stage of these patients was adenocarcinoma in situ, IA, IB, II, and III in 25 (5%), 343 (68.6%), 63 (12.6%), 29 (5.8%), and 40 (8%), respectively. Multivariate analysis showed that the presence of STAS was significantly correlated to higher T (p = 0.001) and N (p = 0.032) stages, moderate/poor differentiation (p = 0.001), and the presence of lymphovascular invasion (p = 0.001). Although positive epidermal growth factor receptor mutation and non-lepidic histologic subtypes were correlated with the presence of STAS in the univariate analysis, they were not significantly correlated with the presence of STAS in the multivariate analysis (p = 0.676 and 0.286, respectively).

CONCLUSIONS

STAS was significantly correlated with several invasive clinicopathological characteristics in surgically resected lung adenocarcinoma. Based on our results and current evidence, the presence of STAS may be considered as a staging profile in future staging system.

Precision Medicine in Non-Small Cell Lung Cancer: Current Standards in Pathology and Biomarker Interpretation

Non-small cell lung cancer (NSCLC) has become a prominent example of precision medicine among solid tumor malignancies. Clinical management of NSCLC now depends on surgical, chemotherapeutic, and radiation treatment regimens based on pathologic findings and clinical staging as well as targeted therapies based on molecular profiling. As molecular testing becomes increasingly important, preserving tissue for this purpose while rendering an accurate histologic diagnosis becomes a key consideration, particularly in advanced-stage NSCLC, in which small biopsy samples or aspirates are often the only specimen available. Next-generation sequencing panels are a powerful method of providing information relevant for both standard-of-care and investigational treatment options. However, taking advantage of the abundance of information gleaned from these panels requires careful annotation, prioritization, and reporting of molecular findings and their clinical significance. Although molecular profiling has traditionally relied on direct sampling of neoplastic tissue, blood-based diagnostics now offer the potential to provide some clinically useful information noninvasively.

Peritumoral radiomics features predict distant metastasis in locally advanced NSCLC

Purpose

Radiomics provides quantitative tissue heterogeneity profiling and is an exciting approach to developing imaging biomarkers in the context of precision medicine. Normal-appearing parenchymal tissues surrounding primary tumors can harbor microscopic disease that leads to increased risk of distant metastasis (DM). This study assesses whether computed-tomography (CT) imaging features of such peritumoral tissues can predict DM in locally advanced non-small cell lung cancer (NSCLC).

Material and methods

200 NSCLC patients of histological adenocarcinoma were included in this study. The investigated lung tissues were tumor rim, defined to be 3mm of tumor and parenchymal tissue on either side of the tumor border and the exterior region extended from 3 to 9mm outside of the tumor. Fifteen stable radiomic features were extracted and evaluated from each of these regions on pre-treatment CT images. For comparison, features from expert-delineated tumor contours were similarly prepared. The patient cohort was separated into training and validation datasets for prognostic power evaluation. Both univariable and multivariable analyses were performed for each region using concordance index (CI).

Results

Univariable analysis reveals that six out of fifteen tumor rim features were significantly prognostic of DM (p-value < 0.05), as were ten features from the visible tumor, and only one of the exterior features was. Multivariablely, a rim radiomic signature achieved the highest prognostic performance in the independent validation sub-cohort (CI = 0.64, p-value = 2.4×10⁻⁵) significantly over a multivariable clinical model (CI = 0.53), a visible tumor radiomics model (CI = 0.59), or an exterior tissue model (CI = 0.55). Furthermore, patient stratification by the combined rim signature and clinical predictor led to a significant improvement on the clinical predictor alone and also outperformed stratification using the combined tumor signature and clinical predictor.

Conclusions

We identified peritumoral rim radiomic features significantly associated with DM. This study demonstrated that peritumoral imaging characteristics may provide additional valuable information over the visible tumor features for patient risk stratification due to cancer metastasis.

Spread Through Air Spaces (STAS): A New Pathologic Morphology in Lung Cancer

In 2015, the World Health Organization classification of lung cancer proposed the concept of spread through air spaces (STAS) as a new pattern of invasion in lung adenocarcinoma. The definition of STAS included one or more pathologic micropapillary clusters, solid nests or single cells beyond the edge of the tumor into air spaces in the surrounding lung parenchyma, and separation from the main tumor other than tumor islands. The roles of STAS has been investigated in many studies. The results indicated that STAS is associated with key clinical variables and the prognosis of patients both in lung adenocarcinoma, lung squamous cell carcinoma, small-cell lung cancer, and lung pleomorphic carcinoma. This mini review will be focused on the developments and perspectives of STAS in lung cancer.

Pulmonary mucinous adenocarcinomas: a clinicopathologic series with emphasis on the prognostic significance of spread through alveolar spaces, and presence of solid growth component

Background

Mucinous adenocarcinoma is often considered a relatively poor prognostic group among adenocarcinomas of the lung and has a high rate of pulmonary recurrence. Pathologic parameters predicting poor outcome have not been extensively studied, including the presence of spread through alveolar spaces (STAS).

Methods

We retrospectively studied time to lung recurrence and time to distant metastasis in 30 mucinous lung tumors, in relationship to histologic parameters, including spread through alveolar spaces, tumor size, invasive size, % invasive size, growth pattern (solid or cribriform, acinar, papillary, micropapillary, and lepidic), type of mucin-producing cell, and TTF-1 positivity.

Results

Median follow-up was 40 months. There were 7 patients (23%) with lung recurrence (mean 22 months) and 7 (23%) with distant metastases (mean 3.7 months). Columnar / goblet cell type was inversely correlated with TTF-1 expression (p = 0.01). The only pathologic parameters associated with outcome were STAS for lung recurrence (p = .005) and solid/cribriform growth (≥ 20% of tumor) for distant metastasis (p = 0.003).

Conclusions

Mucinous adenocarcinomas of the lung are similar to non-mucinous prognostically, in that STAS and solid growth are poor prognosticators, for local and distant recurrence, respectively. The growth patterns of mucinous adenocarcinomas should be reported similar to reporting of non-mucinous adenocarcinomas.

Relationship between MTA1 and spread through air space and their joint influence on prognosis of patients with stage I-III lung adenocarcinoma

OBJECTIVE

To characterize the relationship between metastasis-associated protein 1 (MTA1) and spread through air spaces (STAS), and to investigate the joint prognostic value of MTA1 and STAS in resected lung adenocarcinomas.

METHODS

We retrospectively reviewed 208 operated patients with stage I-III lung adenocarcinoma from January 2009 to December 2014. STAS was identified by H&E staining. Expression level of MTA1 was determined by immunohistochemistry. The relationship between MTA1 and STAS was determined by using a logistic regression model. The synergistic effects of MTA1 and STAS on prognosis were analyzed using a Cox proportional hazards regression model.

RESULTS

Patients with either STAS or high expression of MTA1 had significantly worse overall survival (OS) and shorter recurrence-free survival (RFS) than those without STAS or with low expression of MTA1 (p < 0.001). Among 107 patients with STAS presence in lung adenocarcinomas, 57 (53.3%) cases had high expression of MTA1. High expression of MTA1 was positively associated with the increased frequency of STAS presence (p < 0.01). Subgroup analysis showed that the patients with both high expression of MTA1 and STAS-positive presence had significantly worst OS and shortest RFS compared with the others (p < 0.001), while the patients with high expression of MTA1 /STAS-negative presence shared similar RFS with those with high expression of MTA1 /STAS-positive presence. Furthermore, high MTA1 levels in STAS-positive patients was associated with a higher risk of postoperative metastasis and recurrence (p < 0.001).

CONCLUSIONS

STAS was more frequently observed in adenocarcinomas with high MTA1 expression levels. MTA1 was associated with a higher risk of worse overall survival among patients with STAS and could provide helpful prognostic information in STAS-positive patients with stage I-III lung adenocarcinoma.

Lung Adenocarcinoma: CT Features Associated with Spread through Air Spaces

Purpose To identify the features at CT that are predictive of spread through air spaces (STAS) in surgically resected lung adenocarcinomas. Materials and Methods For this retrospective study, presence of STAS was evaluated in 948 consecutive patients who underwent surgical resection for lung adenocarcinoma from April 2015 to December 2016. Patients who were positive for STAS and negative for STAS were matched at a ratio of 1:2 by using patient variables (age, sex, and smoking status). CT features (ie, percentage of solid component, maximum diameter of solid component, lesion density, location, margin, shape, pseudocavity, calcification, central low attenuation, ill-defined peripheral opacity, air bronchogram, satellite lesions, and pleural retraction) were analyzed by using multivariable logistic regression and receiver operating characteristic curves. Results The final study population consisted of 276 patients (mean age, 59 years; age range, 32-78 years) including 129 men (mean age, 60 years; age range, 36-78 years) and 147 women (mean age, 59 years; age range, 32-78 years). Ninety-two patients were positive for STAS and 184 patients were negative for STAS. STAS was more common in solid tumors (71 of 92; 77%) than in part-solid (21 of 92; 23%) or ground-glass lesions (0 of 92; 0%) (P < .001). STAS was also associated with central low attenuation, ill-defined opacity, air bronchogram, and percentage of solid component (all P < .001). Percentage of solid component was an independent predictor of STAS (odds ratio, 1.06; 95% confidence interval: 1.03, 1.08) and a cut-off value of 90% showed a discriminatory power with a sensitivity of 89.2% and a specificity of 60.3%. Conclusion Percentage of solid component was independently associated with spread through air spaces in lung adenocarcinomas. © RSNA, 2018 Online supplemental material is available for this article.

Significance of spread through air spaces in early-stage lung adenocarcinomas undergoing limited resection

Background

In early‐stage lung adenocarcinomas, spread through air spaces (STAS) are reported to be a prognostic factor in patients who have undergone sublobar resection, but not lobectomy. In contrast, reports have also shown that STAS is significantly associated with poor survival outcomes after lobectomy, but not after limited resection. Thus, the prognostic impact of STAS differs according to published reports.

Methods

A total of 82 patients with early‐stage adenocarcinomas who underwent limited resection and whose STAS status could be examined were enrolled in this retrospective study. We evaluated the association between STAS and clinicopathological characteristics and postoperative survival.

Results

Among 82 patients, 31 (37.8%) were positive for STAS, while 51 (62.2%) were negative. STAS was significantly associated with advanced tumor stage (P < 0.01), lower histological differentiation (P = 0.01), and the presence of pleural invasion (P = 0.01). Patients with STAS had significantly shorter recurrence‐free survival (RFS) and overall survival (OS) than those without STAS (P < 0.01 and P = 0.02, respectively). According to multivariate analysis, positivity for STAS was an independent prognostic parameter for RFS (P < 0.01), but not OS (P = 0.45). Three patients who developed surgical margin recurrence and one patient who developed distant recurrence were all positive for STAS.

Conclusions

STAS was predictive of poor postoperative survival in patients with early‐stage adenocarcinomas treated with limited resection and was associated with surgical margin recurrence.

Pulmonary loose tumor tissue fragments and spread through air spaces (STAS): Invasive pattern or artifact? A critical review

The concept of loose tumor tissue fragments as a pattern of invasion in lung carcinoma has recently been proposed and is included in the 2015 WHO fascicle on the classification of lung tumors, so-called "spread through airs paces" or STAS. This inclusion is controversial, as there are significant data to support that this histologic finding represents an artifact of tissue handling and processing rather than a pattern of invasion. These data are summarized in this review. These data are summarized in this review and support the conclusion that the inclusion of STAS in the WHO classification for lung cancer as a pattern of invasion was premature and erroneous. In our opinion, these tumor cell clusters or loose cells appear to be simply an artifact, although one which may or may not pinpoint to a high-grade tumor with discohesive cells and adverse prognosis.

Tumor Spread Through Air Spaces Identifies a Distinct Subgroup With Poor Prognosis in Surgically Resected Lung Pleomorphic Carcinoma

BACKGROUND

Tumor spread through air spaces (STAS) has recently been reported as a novel form of lung adenocarcinoma invasion that can negatively affect survival; however, its role in pleomorphic carcinoma remains unclear. The goal of this study was to characterize tumor STAS in pleomorphic carcinoma, including its association with clinicopathologic features and prognosis.

METHODS

Tumor specimens obtained from 35 consecutive patients with pleomorphic carcinoma who underwent surgical resection between 2009 and 2015 were reviewed. Tumor STAS was defined as tumor cells spreading within the air spaces in the surrounding lung parenchyma beyond the edge of the primary tumor.

RESULTS

Fourteen patients (40%) had evidence of STAS-positive pleomorphic carcinomas. Three types of morphologic findings were observed: single cells, small tumor cell clusters, and tumor nests. Tumor necrosis tended to be more prevalent in STAS-positive tumors than in STAS-negative tumors (P = .094). Patients with STAS experienced significantly worse recurrence-free survival (P = .005) and overall survival (P = .002) rates than those without STAS. Moreover, multivariate analysis revealed that tumor STAS was an independent risk factor for both recurrence (P = .014) and poor overall survival (P = .042).

CONCLUSIONS

In this first study of its kind, tumor STAS in patients with pleomorphic carcinoma was shown to be associated with high recurrence rates and poor survival after surgical resection. Hence, tumor STAS can serve as a predictor of postoperative survival; this information will enable better risk stratification and more effective clinical management of patients with this rare type of tumor.

Updates on Selected Topics in Lung Cancers: Air Space Invasion in Adenocarcinoma and Ki-67 Staining in Carcinoid Tumors

Context.—

Air space invasion or aerogenous spread of lung adenocarcinoma is a relatively new concept and has been implicated as a potential prognostic factor as well as has been added as an exclusion point in the diagnosis of minimally invasive adenocarcinoma. Potential role for Ki-67 immunostaining as a diagnostic and prognostic marker in pulmonary carcinoid tumors has been suggested in the literature, given the significant interobserver variability and the difficulty in predicting their clinical behavior.

Objective.—

To review the concept of air space invasion in lung adenocarcinoma and the current controversies regarding the role of Ki-67 immunostaining on pulmonary carcinoid tumors

Data Sources.—

PubMed search of English literature.

Conclusions.—

Pathologists need to recognize air space invasion with a critical evaluation to differentiate it from artifacts that are commonly seen in sections. Currently, Ki-67 immunostaining is not recommended for routine use in the diagnosis of pulmonary carcinoid tumors or for predicting their prognosis, except for the differential diagnosis from small cell carcinomas or large cell neuroendocrine carcinomas in small biopsy specimens with crush artifacts.

Shell feature: a new radiomics descriptor for predicting distant failure after radiotherapy in non-small cell lung cancer and cervix cancer

Distant failure is the main cause of human cancer-related mortalities. To develop a model for predicting distant failure in non-small cell lung cancer (NSCLC) and cervix cancer (CC) patients, a shell feature, consisting of outer voxels around the tumor boundary, was constructed using pre-treatment positron emission tomography (PET) images from 48 NSCLC patients received stereotactic body radiation therapy and 52 CC patients underwent external beam radiation therapy and concurrent chemotherapy followed with high-dose-rate intracavitary brachytherapy. The hypothesis behind this feature is that non-invasive and invasive tumors may have different morphologic patterns in the tumor periphery, in turn reflecting the differences in radiological presentations in the PET images. The utility of the shell was evaluated by the support vector machine classifier in comparison with intensity, geometry, gray level co-occurrence matrix-based texture, neighborhood gray tone difference matrix-based texture, and a combination of these four features. The results were assessed in terms of accuracy, sensitivity, specificity, and AUC. Collectively, the shell feature showed better predictive performance than all the other features for distant failure prediction in both NSCLC and CC cohorts.

Significance of Spread Through Air Spaces in Resected Lung Adenocarcinomas With Lymph Node Metastasis

BACKGROUND

Spread through air spaces (STAS) is a recently recognized invasive pattern of lung cancer defined by the World Health Organization as micropapillary clusters, solid nests, or single cells spreading within air spaces beyond the edge of the main tumor. Although STAS has been shown to be a significant prognosticator for the postoperative survival in early-stage lung cancer treated with limited resection, its prognostic impact on the survival in completely resected adenocarcinomas with lymph node metastasis remains unclear.

PATIENTS AND METHODS

STAS was assessed in a total of 63 adenocarcinomas with lymph node metastasis in patients who underwent complete resection. STAS was defined as tumor cells within air spaces in the lung parenchyma beyond the edge of the main tumor. We evaluated the association between STAS and the clinicopathologic characteristics and the postoperative survival.

RESULTS

Among 63 patients, 31 (49.2%) and 32 (50.8%) had disease that was pathologically positive for N1 and N2, respectively. STAS was observed in 45 patients (73.0%) and was not significantly associated with any clinicopathologic characteristics. Patients with the STAS had significantly shorter recurrence-free survival (RFS) but not overall survival than those without STAS (P = .04 and P = .35, respectively). The 5-year RFS in patients with and without STAS was 25.1% and 56.7%, respectively. According to a multivariate analysis, positivity for STAS remained an independent prognostic parameter for RFS (hazard ratio = 3.09; 95% confidence interval, 1.47-7.16; P < .01).

CONCLUSION

STAS was predictive of a poor RFS in completely resected adenocarcinomas with lymph node metastasis.

Spread Through Air Spaces Is a Prognostic Factor in Sublobar Resection of Non-Small Cell Lung Cancer

BACKGROUND

Spread through air spaces (STAS) identified in lung cancer is considered to be a risk factor for recurrence after surgery. The purpose of this study is to clarify the prognostic impact of STAS in sublobar resections.

METHODS

We studied 514 patients with clinical stage IA cancers: 329 underwent lobectomies and 185 underwent sublobar resections. We assessed the prognostic impact of STAS in the cases with a sublobar resection for stage IA lung cancer versus the cases with a lobectomy.

RESULTS

STAS was found in 73 of 329 (22.2%) lobectomy cases and 31 of 185 (16.8%) sublobar resection cases. For overall survival, univariate analysis revealed that STAS was not a prognostic factor in the lobectomy group, but it was a significantly worse prognostic factor for the sublobar resection group in both univariate and multivariate analyses. For the recurrence-free rate, multivariate analysis showed STAS was not a risk factor in the lobectomy group, but it was a significant risk factor for the sublobar resection group in both univariate and multivariate analyses. Patients with STAS and sublobar resection had a significantly higher rate of pulmonary metastases than did patients with STAS and lobectomy (8 of 31 [25.8%] vs 6 of 73 [8.2%]).

CONCLUSIONS

STAS is a prognostic factor of poor outcomes for sublobar resection in patients with lung cancer. The worse prognosis for sublobar resection would be associated with STAS.

Prognostic stratification model for patients with stage I non-small cell lung cancer adenocarcinoma treated with surgical resection without adjuvant therapies using metabolic features measured on F-18 FDG PET and postoperative pathologic factors

PURPOSE

In the management of non-small cell lung cancer (NSCLC), the prognostic stratification of stage I tumors without indication of adjuvant therapy, remains to be elucidated in order to better select patients who can benefit from additional therapies. We aimed to stratify the prognosis of patients with stage I NSCLC adenocarcinoma using clinicopathologic factors and F-18 FDG PET.

MATERIALS AND METHODS

We retrospectively enrolled 128 patients with stage I NSCLC without any high-risk factors, who underwent curative surgical resection without adjuvant therapies. Preoperative clinical and postoperative pathologic factors were evaluated by medical record review. Standardized uptake value corrected with lean body mass (SUL_max) was measured on F-18 FDG PET. Among the factors, independent predictors for recurrence-free survival (RFS) were selected using univariate and stepwise multivariate survival analyses. A prognostic stratification model for RFS was designed using the selected factors.

RESULTS

Tumors recurred in nineteen patients (14.8%). Among the investigated clinicopathologic and FDG PET factors, SUL_max on PET and spread through air spaces (STAS) on pathologic review were determined to be independent prognostic factors for RFS. A prognostic model was designed using these two factors in the following manner: (1) Low-risk: SUL_max ≤ 1.9 and no STAS, (2) intermediate-risk: neither low-risk nor high-risk, (3) high-risk: SUL_max>1.9 and observed STAS. This model exhibited significant predictive power for RFS.

CONCLUSION

We showed that FDG uptake and STAS are significant prognostic markers in stage I NSCLC adenocarcinoma treated with surgical resection without adjuvant therapies.

Current Evidence Does Not Warrant Frozen Section Evaluation for the Presence of Tumor Spread Through Alveolar Spaces

CONTEXT

- Tumor spread through alveolar spaces (STAS) has been correlated with unfavorable prognosis in lung adenocarcinomas treated with sublobar resection, but it is unknown whether STAS can be reliably identified in frozen section (FS) to help stratify patients for lobectomy or sublobar resection.

OBJECTIVE

- To evaluate STAS in FS.

DESIGN

- Tumor spread through alveolar spaces was evaluated in hematoxylin-eosin-stained FS, FS control slides, and all additional slides with lung tissue adjacent to tumor (AdLT) from 48 pT1-2 adenocarcinomas operated on using video-assisted thoracotomy (n = 25) or open thoracotomy (n = 23). The samples included lobectomies (n = 27) and sublobar resections (n = 21). The STAS incidences were compared by FS versus FS control versus AdLT, video-assisted thoracotomy versus open thoracotomy, and lobectomy versus sublobar resection. Sensitivity, specificity, and positive and negative predictive values of STAS⁺ findings were calculated. The literature was queried for best evidence regarding incidence and predictive value of STAS in FS.

RESULTS

- Tumor spread through alveolar spaces positivity was identified in 46 of 48 cases (95.8%), including 23 FS (47.9%), 32 FS control (66.7%), and 43 AdLT (89.6%). The STAS incidence was significantly higher in AdLT than in FS or FS control. Only 2 of the 25 cases that were STAS^- in FS were true negatives. Frozen section sensitivity to detect STAS positivity was 50%, with a 100% positive predictive value and 8% negative predictive value. Systematic literature review identified no evidence regarding STAS identification in FS.

CONCLUSIONS

- The sensitivity and negative predictive value of FS for STAS detection are unacceptably low. There are insufficient data to support intraoperative detection of STAS as a useful predictive feature to help stratify patients for lobectomy or sublobar resections.

Spread through air spaces (STAS): a comprehensive update

The new concept of spread through air spaces (STAS) was introduced for pulmonary adenocarcinomas (ADC) in the 2015 World Health Organization (WHO) classification for lung cancer. Yet available data demonstrate that STAS is of high prognostic impact and associated with specific clinic-pathological characteristics. This article provides a comprehensive overview on recent developments in this field.

A Prospective Study of Loose Tissue Fragments in Non-Small Cell Lung Cancer Resection Specimens: An Alternative View to "Spread Through Air Spaces"

The World Health Organization Classification of Lung Tumors considers "Spread Through Air Spaces" a form of invasion in lung adenocarcinoma. The recently described spread of free-floating cell clusters during lung specimen sectioning, otherwise known as "Spread Through A Knife Surface," represents an ex vivo artifact. The purpose of this study was to prospectively investigate the presence and frequency of these free-floating tumor cell clusters in surgically resected lung cancer specimens and their possible relation to gross examination procedures. A prospective, multi-institutional study of non-small cell lung cancer resection specimen was undertaken. At prosection the first cut was made with a clean knife; the second cut was made in a parallel plane to the first. Four tissue blocks were taken from upper and lower parts of first and second cuts. Hematoxylin and eosin-stained slides were examined for displaced benign and/or malignant tissue fragments. Forty-four resection specimens were studied. The mean number of tumor clusters for blocks 1 to 4 was 0.36, 1.44, 1.86, and 1.95, respectively, and for benign fragments was 0.11, 0.11, 0.13, and 0.25, respectively. Almost all cell clusters were intra-alveolar. Comparison of tumor cell clusters in block 1 with blocks 2 to 4 was significant with P-values (Friedman test for repeated measures 0.03) 0.031, 0.02, and 0.05, respectively. Overall 93% of the loose tissue fragments could be explained by mechanical forces associated with tissue handling. While the 2015 World Health Organization Classification of Lung Tumors recognizes Spread Through Air Spaces as a form of lung cancer invasion, such is debatable and in many instances likely represents mechanical artifact, including dissemination along the prosecting knife blade.

Tumor Spread Through Air Spaces Is an Independent Predictor of Recurrence-free Survival in Patients With Resected Lung Squamous Cell Carcinoma

Tumor spread through air spaces (STAS) is a newly recognized pattern of invasion in lung adenocarcinoma. However, clinical significance of STAS has not yet been characterized in lung squamous cell carcinoma. In this study, we investigated whether STAS could determine clinical outcome in Japanese patients with lung squamous cell carcinoma. We reviewed tumor slides from surgically resected lung squamous cell carcinomas (n=216). STAS was defined as tumor cells within air spaces in the lung parenchyma beyond the edge of the main tumor. Tumors were evaluated for histologic subtypes, tumor budding, and nuclear diameter. Recurrence-free survival (RFS) was analyzed using the log-rank test and the Cox proportional hazards model. Tumor STAS was observed in 87 patients (40%), increasing incidence with lymph node metastasis (P=0.037), higher pathologic stage (P=0.026), and lymphatic invasion (P=0.033). All cases with STAS showed a solid nest pattern. The 5-year RFS for patients with STAS was significantly lower than it was for patients without STAS in all patients (P=0.001) and in stage I patients (n=134; P=0.041). On multivariate analysis, STAS was an independent prognostic factor of a worse RFS (hazard ratio=1.61; P=0.023). Patients with STAS had a significantly increased risk of developing locoregional and distant recurrences (P=0.012 and 0.001, respectively). We found that tumor STAS was an independent predictor of RFS in patients with resected lung squamous cell carcinoma, and it was associated with aggressive tumor behavior.