Distinguishing thymic cysts from low-risk thymomas via [18F]FDG PET/CT

BACKGROUND

Thymic cysts are a rare benign disease that needs to be distinguished from low-risk thymoma. [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) is a non-invasive imaging technique used in the differential diagnosis of thymic epithelial tumours, but its usefulness for thymic cysts remains unclear. Our study evaluated the utility of visual findings and quantitative parameters of [18F]FDG PET/CT for differentiating between thymic cysts and low-risk thymomas.

METHODS

Patients who underwent preoperative [18F]FDG PET/CT followed by thymectomy for a thymic mass were retrospectively analyzed. The visual [18F]FDG PET/CT findings evaluated were PET visual grade, PET central metabolic defect, and CT shape. The quantitative [18F]FDG PET/CT parameters evaluated were PET maximum standardized uptake value (SUVmax), CT diameter (cm), and CT attenuation in Hounsfield units (HU). Findings and parameters for differentiating thymic cysts from low-risk thymomas were assessed using Pearson's chi-square test, the Mann-Whitney U-test, and receiver operating characteristics (ROC) curve analysis.

RESULTS

Seventy patients (18 thymic cysts and 52 low-risk thymomas) were finally included. Visual findings of PET visual grade (P < 0.001) and PET central metabolic defect (P < 0.001) showed significant differences between thymic cysts and low-risk thymomas, but CT shape did not. Among the quantitative parameters, PET SUVmax (P < 0.001), CT diameter (P < 0.001), and CT HU (P = 0.004) showed significant differences. In ROC analysis, PET SUVmax demonstrated the highest area under the curve (AUC) of 0.996 (P < 0.001), with a cut-off of equal to or less than 2.1 having a sensitivity of 100.0% and specificity of 94.2%. The AUC of PET SUVmax was significantly larger than that of CT diameter (P = 0.009) and CT HU (P = 0.004).

CONCLUSIONS

Among the [18F]FDG PET/CT parameters examined, low FDG uptake (SUVmax ≤ 2.1, equal to or less than the mediastinum) is a strong diagnostic marker for a thymic cyst. PET visual grade and central metabolic defect are easily accessible findings.

Mark Wick contributions to pathology of the mediastinum

Mark Wick made a wide range of contributions to the field of mediastinal pathology. Early papers amplified the spectrum of neuroendocrine carcinomas of the thymus and brought attention to the aggressive nature of this tumor, also highlighting the occurrence of coexisting carcinoid tumor and small cell carcinoma of this organ. The controversial issue of thymoma classification was addressed in several papers and editorial comments, while also reporting a case of metastatic thymoma. A series of thymic carcinomas as well a report on the unusual clear cell variant bear his name as one of the authors. He summarized the topic of mediastinal cyst in a review published in 2005. Sarcomas arising in mediastinal germ cell tumors were also within the purview of his interests, with a publication of series of seven cases. He reviewed the topic of inflammatory myofibroblastic tumor of the heart and added a case to the existing literature. Two books dedicated to different aspect of mediastinal pathology also carry his name in the front cover in association with Drs Taazelar in one and Marchevsky in the other.

On the Histologic Classification of Thymoma

The classification of thymoma continues to be a source of controversy in pathology. The difficulties in histologic classification are evident from the number of proposals that have been offered over the years, as well as for the continuous changes and modifications introduced by the World Health Organization to their classification system over the past 20 years. We analyze here some of the issues involved in the classification of these tumors and the difficulties encountered for practicing pathologists in deciphering the "letters and numbers" system devised by the World Health Organization. We would like to propose an alternate approach to thymoma histologic classification that capitalizes on the basic observation of their cytologic features and incorporates the pattern of growth resulting from the interplay of the tumor cells with other cellular constituents as a secondary characteristic. The proposed histologic classification provides a simplified, reproducible means of histologically categorizing these tumors and can be easily understood by most practicing pathologists in simple and clear morphologic terms.

Superiority of [68Ga]Ga-DOTA-FAPI-04 PET/CT to [18F]FDG PET/CT in the evaluation of thymic epithelial tumours

PURPOSE

The purpose of this study is to compare the ability of [68Ga]Ga-DOTA-FAPI-04 PET/CT and [18F]FDG PET/CT to stratify the malignancy and invasiveness of thymic epithelial tumours (TETs).

METHODS

From April 2021 to November 2022, participants with suspected TETs confirmed by histopathology or follow-up imaging were prospectively analysed. All participants underwent [18F]FDG and [68Ga]Ga-DOTA-FAPI-04 PET/CT within 1 week. Clinical characteristics, CT features, and metabolic parameters (maximum standardized uptake value [SUVmax] and tumour-to-mediastinum ratio [TMR]) of subjects with different pathological types and stages were compared. The diagnostic capacities of [18F]FDG and [68Ga]Ga-DOTA-FAPI-04 PET/CT were compared using receiver operating characteristic (ROC) curves and McNemar's test.

RESULTS

Fifty-seven participants were included. [68Ga]Ga-DOTA-FAPI-04 PET/CT was superior to [18F]FDG PET/CT in differentiating thymomas from thymic carcinomas (TCs) (AUC: 0.99 vs. 0.90, P = 0.02). Logistic regression revealed that SUVmax-FAPI (P = 0.04) was a significant predictive factor for TCs. SUVmax-FAPI and TMR-FAPI showed an excellent ability to differentiate low-risk thymomas (types A, AB, and B1), high-risk thymomas (types B2 and B3), and TCs (both P < 0.001). In thymomas, only SUVmax-FAPI (P < 0.001), TMR-FAPI (P < 0.001), and nonsmooth edges (P = 0.02) were significantly higher in the advanced-stage (Masaoka-Koga [MK] stage III/IV) group than in the early-stage group (MK stage I/II). Compared with [18F]FDG PET/CT, [68Ga]Ga-DOTA-FAPI-04 PET/CT showed significantly higher specificity (67% [46 of 69] vs. 93% [64 of 69], P < 0.001) in the detection of lymph node metastases and higher sensitivity (49% [19 of 39] vs. 97% [38 of 39], P < 0.001) in evaluating distant metastases. Both SUVmax-FAPI and TMR-FAPI were correlated with FAP expression (both r = 0.843, P < 0.001).

CONCLUSION

[68Ga]Ga-DOTA-FAPI-04 PET/CT was superior to [18F]FDG PET/CT in evaluating the World Health Organization (WHO) classification, MK staging, and metastatic status of TETs.

TRIAL REGISTRATION

ChiCTR2000038080, registration date 2020-09-09, https://www.chictr.org.cn/com/25/showproj.aspx?proj=61192.

Prognostic factors and role of postoperative radiotherapy in surgically resected thymomas

Objective

To investigate the prognostic factors in and role of postoperative radiotherapy (PORT) for surgically resected thymomas.

Methods

A total of 1540 patients with pathologically confirmed thymomas undergoing resection between 2000 and 2018 were identified retrospectively from the SEER (Surveillance, Epidemiology, and End Results) database. Tumors were restaged as local (limited to thymus), regional (invasion to mediastinal fat and other neighboring structures), or distant stage. Disease-specific survival (DSS) and overall survival (OS) were estimated by the Kaplan-Meier method and the log-rank test. Adjusted hazard ratios (HRs) with 95% CIs were calculated by Cox proportional hazards modeling.

Results

Tumor stage and histology were independent predictors of both DSS (regional: HR, 3.711; 95% CI, 2.006-6.864; distant: HR, 7.920; 95% CI, 4.061-15.446; type B2/B3: HR, 1.435; 95% CI, 1.008-2.044) and OS (regional: HR, 1.461; 95% CI, 1.139-1.875; distant: HR, 2.551; 95% CI, 1.855-3.509; type B2/B3: HR, 1.409; 95% CI, 1.153-1.723). For patients with regional stage and type B2/B3 thymomas, PORT was associated with better DSS after thymectomy/thymomectomy (HR, 0.268; 95% CI, 0.099-0.727), but the association was not significant after extended thymectomy (HR, 1.514; 95% CI, 0.516-4.44). Among patients with lymph node metastases, those who received PORT (HR, 0.372; 95% CI, 0.146-0.949), chemotherapy (HR, 0.843; 95% CI, 0.303-2.346), or both (HR, 0.296, 95% CI, 0.071-1.236) had a better OS.

Conclusions

The extent of invasion and tumor histology were independent predictors of worse survival following surgical resection of thymoma. Patients with regional invasion and type B2/B3 thymoma who undergo thymectomy/thymomectomy may benefit from PORT, while patients with nodal metastases may benefit from multimodal therapy, including PORT and chemotherapy.

Is PET/CT Able to Predict Histology in Thymic Epithelial Tumours? A Narrative Review

BACKGROUND

The usefulness of ¹⁸FDG PET/CT scan in the evaluation of thymic epithelial tumours (TETs) has been reported by several authors, but data are still limited and its application in clinical practice is far from being defined.

METHODS

We performed a narrative review of pertinent literature in order to clarify the role of ¹⁸FDG PET/CT in the prediction of TET histology and to discuss clinical implications and future perspectives.

RESULTS

There is only little evidence that ¹⁸FDG PET/CT scan may distinguish thymic hyperplasia from thymic epithelial tumours. On the other hand, it seems to discriminate well thymomas from carcinomas and, even more, to predict the grade of malignancy (WHO classes). To this end, SUVmax and other PET variables (i.e., the ratio between SUVmax and tumour dimensions) have been adopted, with good results. Finally, however promising, the future of PET/CT and theranostics in TETs is far from being defined; more robust analysis of imaging texture on thymic neoplasms, as well as new exploratory studies with "stromal PET tracers," are ongoing.

CONCLUSIONS

PET may play a role in predicting histology in TETs and help physicians in the management of these insidious malignancies.

Comparison of Efficacy and Safety of Platinum-Based Chemotherapy as First-Line Therapy between B3 Thymoma and Thymic Carcinoma

BACKGROUND

B3 type thymoma is defined as a well-differentiated thymic carcinoma and is similar to a thymic carcinoma. However, the differences between them are not well defined. In addition, the data to compare the efficacy and safety of platinum-based chemotherapy as first-line therapy between B3 thymoma and thymic carcinoma are lacking.

METHODS

The efficacy and safety of platinum-based chemotherapy as first-line therapy was retrospectively compared between a group of 36 patients with type B3 thymoma and a group of 127 patients with thymic carcinoma treated between January 2009 and March 2022 at the Zhejiang Cancer Hospital. Objective response rate (ORR), progression-free survival (PFS), overall survival (OS), and treatment-related adverse events were analyzed.

RESULTS

The ORRs for B3 thymoma and thymic carcinoma were 36.1% and 28.3%, respectively (p = 0.370). Among all patients, the difference in PFS between B3 thymoma and thymic carcinoma was not significant (11.3 vs. 10.1 months, p = 0.118). The squamous carcinoma subgroup did not exhibit any differences in PFS compared to B3 thymoma (11.7 vs. 11.3 months, p = 0.161). The result for the non-squamous carcinoma subgroup was similar (6.5 vs. 11.3 months, p = 0.128). Furthermore, the OS values for B3 thymoma and thymic carcinoma were not significantly different (58.3 vs. 35.1 months, p = 0.067). However, there were differences in OS between B3 thymoma and non-squamous carcinoma (58.3 vs. 30.6 months, p = 0.031).

CONCLUSIONS

B3 thymoma and especially squamous carcinoma patients may be treated using a similar therapy scheme as that utilized for thymic carcinoma.

Atypical thymomas with squamoid and spindle cell features: clinicopathologic, immunohistochemical and molecular genetic study of 120 cases with long-term follow-up

Thymomas are rare tumors characterized by a broad range of morphologic appearances that can sometimes give rise to difficulties for classification. We have studied a series of 120 thymoma patients in whom the tumors were characterized by sheets of atypical epithelial cells with squamoid and/or spindle cell features. They occurred in 63 men and 57 women and presented as a discrete mass in the anterior mediastinum measuring 2-23 cm (mean: 8.2 cm). Patients' ages ranged from 14 to 86 years (mean: 57.8) and most had symptoms referable to a mass lesion. 20 patients had myasthenia gravis or other autoimmune disorder. 76 cases were characterized by a predominant population of round to polygonal tumor cells while 32 cases were characterized by atypical oval or spindle cells. 12 cases showed mixed features and 16 cases showed the development of thymic carcinoma arising from thymoma. All cases were positive for p40/p63 and cytokeratin AE1/AE3. 23 cases were positive for CD5 (25%), and 13 for CD117 (14%). MIB1 showed a significant increase in proliferative activity (mean = 11.6%). Next generation sequencing in 47 cases did not disclose any variants amenable to current targeted therapies. Clinical follow up ranging from 2 to 29 years showed a progressive increase in aggressive behavior and fatality rate with advancing stage. Overall survival was 87% at 5 years, 67% at 10 years, and 23% at 20 years. Completeness of resection and staging were the most significant parameters for survival. The more aggressive tumors followed a protracted clinical course with multiple recurrences and metastases over a long period of time (mean = 19.8 years from time of initial relapse to death). Atypical thymomas are a distinct category of thymic epithelial neoplasm characterized by a slowly progressive clinical course with increased potential for metastases, transformation to a higher-grade malignancy, and fatal outcome in some cases.

An Overview of Surgical Treatment of Thymic Epithelial Tumors in Korea: A Retrospective Multicenter Analysis

Background

Thymic epithelial tumors (TETs) are rare, and information regarding their surgical outcomes and prognostic factors has rapidly changed in the past few decades. We analyzed surgical treatment practices for TETs and outcomes in terms of overall survival (OS) and freedom from recurrence (FFR) during a 13-year period in Korea.

Methods

In total, 1,298 patients with surgically resected TETs between 2000 and 2013 were enrolled retrospectively. OS and FFR were calculated using the Kaplan-Meier method and evaluated with the log-rank test. Prognostic factors for OS and FFR were analyzed with multivariable Cox regression.

Results

A total of 1,098 patients were diagnosed with thymoma, and 200 patients were diagnosed with thymic carcinoma. Over the study period, the total number of patients with surgically treated TETs and the proportion of patients who underwent minimally invasive thymic surgery (MITS) increased annually. The 5-year and 10-year survival rates of surgically treated TETs were 91.0% and 82.1%, respectively. The 5-year and 10-year recurrence rates were 86.3% and 80.0%, respectively. The outcomes of surgically treated TETs improved over time. Multivariable Cox hazards analysis for OS, age, tumor size, and Masaoka-Koga stage were independent predictors of prognosis. The World Health Organization classification and tumor-node-metastasis (TNM) staging were also related to the prognosis of TETs.

Conclusion

Surgical treatment of TETs achieved a good prognosis with a recent increase in MITS. The M-K stage was the most important prognostic factor for OS and FFR. The new TNM stage could also be an effective predictor of the outcomes of TETs.

Diagnostic Test Accuracy of 18F-FDG PET or PET/CT for Characterization of Histologic Type of Thymic Epithelial Tumor: A Meta-analysis

PURPOSE

This study investigated diagnostic accuracies of 18F-FDG PET or PET/CT for characterization of histologic type of thymic epithelial tumors (TETs) through a systematic review and meta-analysis.

PATIENTS AND METHODS

The PubMed, Cochrane database, and EMBASE database, from the earliest available date of indexing through August 31, 2020, were searched for studies evaluating diagnostic performance of 18F-FDG PET or PET/CT for characterization of TET. We determined the sensitivities and specificities, calculated positive and negative likelihood ratios (LR+ and LR-), and constructed summary receiver operating characteristic curves.

RESULTS

The pooled sensitivity of 18F-FDG PET or PET/CT was 0.89 (95% confidence interval [CI], 0.80-0.95), and the pooled specificity was 0.77 (95% CI, 0.63-0.87) for differentiation between thymic cancer and thymoma. Likelihood ratio syntheses gave an overall positive likelihood ratio (LR+) of 3.9 and negative likelihood ratio (LR-) of 0.14. The pooled diagnostic odds ratio was 28 (95% CI, 13-63). The pooled sensitivity was 0.90 (95% CI, 0.75-0.96), and the pooled specificity was 0.81 (95% CI, 0.68-0.89) for differential diagnosis of a low-risk or high-risk TET. LR+ was 4.7 and LR- was 0.12. The pooled diagnostic odds ratio was 38 (95% CI, 12-121). In meta-regression analysis, no variable was the source of the study heterogeneity.

CONCLUSIONS

18F-FDG PET or PET/CT has excellent diagnostic performances for characterization of TET. Further large multicenter studies would be necessary to establish the diagnostic accuracy of 18F-FDG PET or PET/CT for differentiation of histologic type of TET.

Current Roles of PET/CT in Thymic Epithelial Tumours: Which Evidences and Which Prospects? A Pictorial Review

Simple Summary

Thymic epithelial tumours are uncommon malignancies. Histologically, they may be distinguished in different subtypes and different relapse risk classes. Surgery, sometimes after induction therapy, stays the best treatment option, and long-term results depend on the disease stage and completeness of resection. In this context, ¹⁸F FDG PET CT scan has been reported to play different roles in the care strategy of thymic epithelial tumours. In the present review, we analyse current evidences, the use of this imaging tool and future application prospects.

Abstract

Background: The use of ¹⁸F FDG PET/CT scan in thymic epithelial tumours (TET) has been reported in the last two decades, but its application in different clinical settings has not been clearly defined. Methods: We performed a pictorial review of pertinent literature to describe different roles and applications of this imaging tool to manage TET patients. Finally, we summarized future prospects and potential innovative applications of PET in these neoplasms. Results: ¹⁸FFDG PET/CT scan may be of help to distinguish thymic hyperplasia from thymic epithelial tumours but evidences are almost weak. On the contrary, this imaging tool seems to be very performant to predict the grade of malignancy, to a lesser extent pathological response after induction therapy, Masaoka Koga stage of disease and long-term prognosis. Several other radiotracers have some application in TETs but results are limited and almost controversial. Finally, the future of PET/CT and theranostics in TETs is still to be defined but more detailed analysis of metabolic data (such as texture analysis applied on thymic neoplasms), along with promising preclinical and clinical results from new “stromal PET tracers”, leave us an increasingly optimistic outlook. Conclusions: PET plays different roles in the management of thymic epithelial tumours, and its applications may be of help for physicians in different clinical settings.

Diagnostic and prognostic values of 2-[18F]FDG PET/CT in resectable thymic epithelial tumour

OBJECTIVES

We aimed to evaluate the diagnostic ability for the prediction of histologic grades and prognostic values on recurrence and death of pretreatment 2-[¹⁸F]FDG PET/CT in patients with resectable thymic epithelial tumours (TETs).

METHODS

One hundred and fourteen patients with TETs who underwent pretreatment 2-[¹⁸F]FDG PET/CT between 2012 and 2018 were retrospectively evaluated. TETs were classified into three histologic subtypes: low-risk thymoma (LRT, WHO classification A/AB/B1), high-risk thymoma (HRT, B2/B3), and thymic carcinoma (TC). Area under the receiver operating characteristics curve (AUC) was used to assess the diagnostic performance of PET/CT variables (maximum standardised uptake value [SUVmax], metabolic tumour volume [MTV], total lesion glycolysis [TLG], maximum diameter). Cox proportional hazards models were built using PET/CT and clinical variables.

RESULTS

The tumours included 52 LRT, 33 HRT, and 29 TC. SUVmax showed good diagnostic ability for differentiating HRT/TC from LRT (AUC 0.84, 95% confidence interval [CI] 0.76 - 0.92) and excellent ability for differentiating TC from LRT/HRT (AUC 0.94, 95% CI 0.90 - 0.98), with significantly higher values than MTV, TLG, and maximum diameter. With an optimal cut-off value of 6.4, the sensitivity, specificity, and accuracy for differentiating TC from LRT/HRT were 69%, 96%, and 89%, respectively. In the multivariable Cox proportional hazards analyses for freedom-from-recurrence, SUVmax was an independent prognostic factor (p < 0.001), whereas MTV and TLG were not. SUVmax was a significant predictor for overall survival in conjunction with clinical stage and resection margin.

CONCLUSION

SUVmax showed excellent diagnostic performance for prediction of TC and significant prognostic value in terms of recurrence and survival.

KEY POINTS

• Maximum standardised uptake value (SUVmax) shows excellent performance in the differentiation of thymic carcinoma from low- and high-risk thymoma. • SUVmax is an independent prognostic factor for freedom-from-recurrence in the multivariable Cox proportional hazard model and a significant predictor for overall survival. • 2-[¹⁸F]FDG PET/CT can provide a useful diagnostic and prognostic imaging biomarker in conjunction with histologic classification and stage and help choose appropriate management for thymic epithelial tumours.

Value of 18F-FDG PET/computed tomography in predicting the simplified WHO grade of malignancy in thymic epithelial tumors

OBJECTIVE

To investigate the value of 18F-fluorodeoxyglucose (F-FDG) PET/computed tomography (CT) in predicting the simplified WHO grade of malignancy in thymic epithelial tumors.

MATERIALS AND METHODS

We retrospectively reviewed 81 patients with pathologically proven thymic epithelial tumors who underwent F-FDG PET/CT before surgical resection. Maximum standardized uptake value (SUVmax) and SUVmax/tumor size were measured on the primary lesion. A receiver operating characteristics (ROC) curve were performed for assessing the ability of F-FDG PET/CT as a predictor of the simplified WHO classification.

RESULTS

There were 43 male patients (53.1%) and 38 female patients (46.9%), and the mean age was 55.6 ± 11.9 years. The mean tumor size was 53.2 ± 21.4 mm. There were 24 low-risk thymomas (29.6%) (A, AB, and B1), 29 high-risk thymomas (35.8%) (B2 and B3), and 28 thymic carcinomas (34.6%). The SUVmax and SUVmax/tumor size were found to be predictive factors that were useful to distinguish thymomas and thymic carcinomas, and area under the ROC curve were 0.820 and 0.691, respectively (P < 0.05), and the cutoff value for discriminating thymomas and thymic carcinomas was 5.34.

CONCLUSION

In conclusion, a significant relationship was observed between SUVmax, SUVmax/tumor size and histological WHO classification of thymic epithelial tumors. F-FDG PET/CT may be useful for predicting the grade of malignancy in thymic epithelial.

Usefulness of Preoperative 18F-FDG PET/CT for Patients with Thymic Epithelial Tumors

Background

The purpose of this study was to investigate the relationship between preoperative FDG-PET parameters and the World Health Organization (WHO) classification or Masaoka staging system of thymic epithelial tumors.

Methods

We retrospectively reviewed 32 patients with histologically proven thymic epithelial tumors who underwent FDG-PET/CT before surgical resection. FDG-PET parameters, including the maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolytic activity (TLG), were measured. These PET parameters were compared in the Masaoka staging system and WHO classification. A receiver operating characteristics (ROC) analysis was performed to identify the cut-off values of PET parameters for the accurate differentiation of early and advanced stages in the Masaoka staging system.

Results

There were 17 low-risk thymomas (1 type A, 9 type AB, and 7 type B1), 8 high-risk thymomas (4 type B2 and 4 type B3), and 7 thymic carcinomas (7 squamous cell carcinoma). Their Masaoka stages were as follows: 24 in the early stage (stages I and II) and 8 in the advanced stage (stage III). Regarding the WHO classification, only SUVmax showed a significant difference (P < 0.05). In the Masaoka stage, all PET parameters were significantly higher in the advanced stage than in the early stage (P < 0.05). In the ROC analysis to predict the early and advanced stages in thymic epithelial tumors, the area under the curve was the highest for TLG among the PET parameters examined and the cut-off value of TLG for discriminating the early from advanced stage with maximal sensitivity and specificity was 30.735.

Conclusion

Although volumetric PET parameters, such as MTV and TLG, did not correlate with the WHO classification, a significant correlation was observed between SUVmax and the WHO classification. In the Masaoka staging system, volumetric PET parameters may achieve more precise staging than SUVmax.

High CTLA-4 expression correlates with poor prognosis in thymoma patients

Thymomas, tumors that arise from epithelial cells of the thymus gland, are the most common neoplasms of the anterior mediastinum, with an incidence rate of approximately 2.5 per million/year. Cytotoxic T Lymphocyte Antigen 4 (CTLA-4 or CD152) exerts inhibitory activity on T cells, and since its oncogenic role in the progression of different types of tumors, it has emerged as a potential therapeutic target in cancer patients.

In this study, we assessed the expression of CTLA-4 both at mRNA and protein levels in paraffin embedded-tissues from patients with thymomas. Furthermore, we evaluated the relationship between CTLA-4 expression and the clinical-pathologic characteristics and prognosis in patients with thymomas. Sixty-eight patients with median age corresponding to 62 years were included in this analysis. Thymomas were classified accordingly to the WHO and Masaoka-Koga for histochemical analysis and for prognostic significance.

A statistical difference was found between CTLA-4 mRNA levels in human normal thymus compared with thymoma specimens. CTLA-4 expression was statistically found to progressively increase in A, B1, B2, AB and it was maximal in B3 thymomas. According to Masaoka-Koga pathological classification, CTLA-4 expression was lower in I, IIA and IIB, and higher in invasive III and IV stages. By confocal microscopy analysis we identified the expression of CTLA-4 both in tumor cells and in CD45⁺ tumor-infiltrating leukocytes, mainly in B3 and AB thymomas.

Finally, CTLA-4 overexpression significantly correlates with reduced overall survival in thymoma patients and in atypical thymoma subgroup, suggesting that it represents a negative prognostic factor.

PD-1 and PD-L1 expression in thymic epithelial tumours and non-neoplastic thymus

Aims

We explored the relationships between programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) expression and the pathological and clinical features of thymic epithelial tumours and thymic hyperplasia.

Methods

We evaluated PD-1 and PDL-1 expressions within epithelial and microenvironmental components in thymic epithelial tumours (n=44) and thymic hyperplasias (n=8), immunohistochemically. We compared the results with demographic, clinical and histopathological features of the cases.

Results

We found 48% epithelial expression and 82.7% microenvironment expression for PD-1 and 11.5% epithelial expression and 34.6% microenvironment expression for PD-L1. There was no PD-1 expression, in either the epithelial or microenvironment, in the thymic hyperplasia group. PD-1 and PD-L1 positivity was more significant in thymic epithelial tumours than thymic hyperplasia. Patients with PD-1-positive microenvironments exhibited significantly shorter mean estimated survival time than their negative counterparts.

Conclusion

These findings suggest that anti-PD-1 and anti-PD-L1 therapies may benefit patients due to high release of PD-1 and PD-L1 in thymic epithelial tumours.

Can 18F-FDG PET predict the grade of malignancy in thymic epithelial tumors? An evaluation of only resected tumors

Objective

Although 18-fluorine fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) is thought to be useful for predicting the histological grade of thymic epithelial tumors (TETs), it remains controversial. To date, just a few of many previous studies have included only resected cases. Therefore, we investigated ¹⁸F-FDG PET findings only in patients with resected TETs.

Patients and methods

A total of 112 patients with TETs consisting of 92 thymomas and 20 thymic carcinomas (TCs), resected at two institutes (Shizuoka Cancer Center [Shizuoka] and National Cancer Center Hospital [Tokyo]) between October 2002 and December 2015, were evaluated. Spearman rank correlation coefficient was used to assess the association between the maximum standardized uptake value (SUVmax) in the tumor and both the histological subtype and tumor stage. The cutoff value of SUVmax for differentiating thymoma from TC was calculated.

Results

The SUVmax was strongly related to both the World Health Organization (WHO) histological subtype and tumor stage based on the eighth edition of the tumor-node-metastasis (TNM) classification (Spearman rank correlation coefficient =0.485 and 0.432; p = 0.000 and 0.000, respectively). There was a significant difference between thymoma and TC. The optimal SUVmax cutoff value for differentiating thymoma from TC was 4.58 (sensitivity: 80% and specificity: 78.3%). In contrast, there was no significant difference between low-risk (type A, AB, and B1) and high-risk (type B2 and B3) thymoma, or between type B3 thymoma and the other subtypes.

Conclusion

Our results suggest that ¹⁸F-FDG PET is useful for differentiating thymoma from TC, but not for predicting the histologic grade of thymoma.

Invasive Medullary Type A Thymoma With Recurrent Distant Metastases

Thymomas are rare epithelial mediastinal tumors showing a certain propensity for local and intrathoracic recurrences. Otherwise, extrathoracic metastases are very rarely reported and are usually associated with type B thymomas or thymic carcinomas. We present a challenging patient with an invasive (Masaoka-Koga stage IIb) medullary type A thymoma with recurrent extrathoracic metastases (pulmonary and vertebral localizations occurring 2 and 7 years after the initial radical thymectomy, respectively). Despite type A thymoma being considered a low-grade malignancy with a scarce propensity to recurrence, the present case should alert clinicians to the possibility of bone metastasis. Long-term follow-up in this slow-growing neoplasm is then mandatory.

Postoperative radiotherapy and tumor recurrence after complete resection of stage II/III thymic tumor: a meta-analysis of cohort studies

BACKGROUND

Whether postoperative radiotherapy (PORT) is effective for reducing the recurrence risk in patients who received complete resection of the stage II or III thymic tumors has not been determined. A meta-analysis was performed by combining the results of all available controlled trials.

METHODS

PubMed, Cochrane's Library, and the Embase databases were searched for studies which compared the recurrence data for patients with complete resection of the stage II or III thymic tumors assigned to an observing group, or a PORT group. A random effect model was applied to combine the results.

RESULTS

Nineteen studies, all designed as retrospective cohort studies were included. These studies included 663 patients of PORT group and 617 patients of observing group. The recurrence rate for the patients in PORT group and observing group were 12.4% and 11.5%, respectively. Results of our study indicated that PORT has no significant influence on recurrent risk in patients with stage II or III thymic tumor after complete resection (odds ratio 1.02, 95% confidence interval 0.55-1.90, P=0.96). When stratified by stages, our meta-analyses did not indicate any significant effects of PORT on recurrent outcomes in either the stage II or the stage III patients. Moreover, subsequent analysis limited to studies only including patients with thymoma or thymic carcinoma also did not support the benefits of PORT on recurrent outcomes.

CONCLUSION

Although derived from retrospective cohort studies, current evidence did not support any benefit of PORT on recurrent risk in patients with complete resection of the stage II or III thymic tumors.

Clinicopathological analysis of 241 thymic epithelial tumors-experience in the Shanghai Chest Hospital from 1997-2004

BACKGROUND

To assess the correlation of WHO histological classification of thymomas and thymic carcinomas (TCs) with prognosis in recently treated patient cohort compared to a historical one from a single institution.

METHODS

Retrospective review of clinical charts and histological sections of 241 patients treated during 1997-2004. Univariate and multivariate analysis of associations between risk factors including gender, age, tumor size, myasthenia gravis, WHO histological subtype, Masaoka stage, resection status, (neo-)adjuvant therapies, and survival.

RESULTS

The 5-year overall survival (OS) of A, AB, B1, B2, B3 thymomas and TCs patients was 100%, 100%, 94%, 80%, 94% and 45%. Five-year progression-free survival (PFS) was 100%, 96%, 78%, 80%, 78% and 39%, respectively. The 5-year OS of patients with Masaoka stage I, II, III and IV thymomas and TCs was 96%, 89%, 59% and 50%. (Neo-)adjuvant therapies were administered more often than in the historical cohort. Tumor-related death mainly occurred in patients with stage III, IV and B2, B3 thymomas and TCs. By univariate analysis, gender, tumor size, myasthenia gravis (MG) status, histotype, Masaoka stage, resection status and treatment were associated with OS. By multivariate analysis, histological subtype, Masaoka stage, and (neo-)adjuvant therapy were revealed as independent prognostic indicators.

CONCLUSIONS

WHO histological subtype, Masaoka stage and (neo-)adjuvant treatment have remained independent determinants of OS in patients with thymomas and TCs. Compared with the historical cohort during 1969-1996, prognosis of patients with B2, B3 thymomas has improved, which may be partly due to the increased use of adjuvant therapies. Prognosis of patients with TCs remained unsatisfactory, suggesting that neoadjuvant treatment should be tested to improve survival.

Differentiating the grades of thymic epithelial tumor malignancy using textural features of intratumoral heterogeneity via (18)F-FDG PET/CT

OBJECTIVE

We aimed to explore the ability of textural heterogeneity indices determined by (18)F-FDG PET/CT for grading the malignancy of thymic epithelial tumors (TETs).

METHODS

We retrospectively enrolled 47 patients with pathologically proven TETs who underwent pre-treatment (18)F-FDG PET/CT. TETs were classified by pathological results into three subgroups with increasing grades of malignancy: low-risk thymoma (LRT; WHO classification A, AB and B1), high-risk thymoma (B2 and B3), and thymic carcinoma (TC). Using (18)F-FDG PET/CT, we obtained conventional imaging indices including SUVmax and 20 intratumoral heterogeneity indices: i.e., four local-scale indices derived from the neighborhood gray-tone difference matrix (NGTDM), eight regional-scale indices from the gray-level run-length matrix (GLRLM), and eight regional-scale indices from the gray-level size zone matrix (GLSZM). Area under the receiver operating characteristic curve (AUC) was used to demonstrate the abilities of the imaging indices for differentiating subgroups. Multivariable logistic regression analysis was performed to show the independent significance of the textural indices. Combined criteria using optimal cutoff values of the SUVmax and a best-performing heterogeneity index were applied to investigate whether they improved differentiation between the subgroups.

RESULTS

Most of the GLRLM and GLSZM indices and the SUVmax showed good or fair discrimination (AUC >0.7) with best performance for some of the GLRLM indices and the SUVmax, whereas the NGTDM indices showed relatively inferior performance. The discriminative ability of some of the GLSZM indices was independent from that of SUVmax in multivariate analysis. Combined use of the SUVmax and a GLSZM index improved positive predictive values for LRT and TC.

CONCLUSIONS

Texture analysis of (18)F-FDG PET/CT scans has the potential to differentiate between TET tumor grades; regional-scale indices from GLRLM and GLSZM perform better than local-scale indices from the NGTDM. The SUVmax and heterogeneity indices may have complementary value in differentiating TET subgroups.

cFLIP overexpression in T cells in thymoma-associated myasthenia gravis

Objective

The capacity of thymomas to generate mature CD4+ effector T cells from immature precursors inside the tumor and export them to the blood is associated with thymoma-associated myasthenia gravis (TAMG). Why TAMG(+) thymomas generate and export more mature CD4+ T cells than MG(−) thymomas is unknown.

Methods

Unfixed thymoma tissue, thymocytes derived thereof, peripheral blood mononuclear cells (PBMCs), T-cell subsets and B cells were analysed using qRT-PCR and western blotting. Survival of PBMCs was measured by MTT assay. FAS-mediated apoptosis in PBMCs was quantified by flow cytometry. NF-κB in PBMCs was inhibited by the NF-κB-Inhibitor, EF24 prior to FAS-Ligand (FASLG) treatment for apoptosis induction.

Results

Expression levels of the apoptosis inhibitor cellular FLICE-like inhibitory protein (c-FLIP) in blood T cells and intratumorous thymocytes were higher in TAMG(+) than in MG(−) thymomas and non-neoplastic thymic remnants. Thymocytes and PBMCs of TAMG patients showed nuclear NF-κB accumulation and apoptosis resistance to FASLG stimulation that was sensitive to NF-κB blockade. Thymoma removal reduced cFLIP expression in PBMCs.

Interpretation

We conclude that thymomas induce cFLIP overexpression in thymocytes and their progeny, blood T cells. We suggest that the stronger cFLIP overexpression in TAMG(+) compared to MG(−) thymomas allows for the more efficient generation of mature CD4+ T cells in TAMG(+) thymomas. cFLIP overexpression in thymocytes and exported CD4+ T cells of patients with TAMG might contribute to the pathogenesis of TAMG by impairing central and peripheral T-cell tolerance.

ITMIG consensus statement on the use of the WHO histological classification of thymoma and thymic carcinoma: refined definitions, histological criteria, and reporting

INTRODUCTION

The 2004 version of the World Health Organization classification subdivides thymic epithelial tumors into A, AB, B1, B2, and B3 (and rare other) thymomas and thymic carcinomas (TC). Due to a morphological continuum between some thymoma subtypes and some morphological overlap between thymomas and TC, a variable proportion of cases may pose problems in classification, contributing to the poor interobserver reproducibility in some studies.

METHODS

To overcome this problem, hematoxylin-eosin-stained and immunohistochemically processed sections of prototypic, "borderland," and "combined" thymomas and TC (n = 72) were studied by 18 pathologists at an international consensus slide workshop supported by the International Thymic Malignancy Interest Group.

RESULTS

Consensus was achieved on refined criteria for decision making at the A/AB borderland, the distinction between B1, B2, and B3 thymomas and the separation of B3 thymomas from TCs. "Atypical type A thymoma" is tentatively proposed as a new type A thymoma variant. New reporting strategies for tumors with more than one histological pattern are proposed.

CONCLUSION

These guidelines can set the stage for reproducibility studies and the design of a clinically meaningful grading system for thymic epithelial tumors.

Evidence-based pathology: systematic literature reviews as the basis for guidelines and best practices

CONTEXT

Evidence-based medicine has been proposed as a new paradigm for the identification and evaluation of medical information. Best available evidence or data are identified and used as the basis for the diagnosis and treatment of individual patients. Evidence-based pathology has adapted basic evidence-based medicine concepts to the specific needs of pathology and laboratory medicine.

OBJECTIVES

To briefly review the history and basic concepts of evidence-based medicine and evidence-based pathology, describe how to perform and interpret systematic reviews, and discuss how to integrate best evidence into guidelines.

DATA SOURCES

PubMed (National Library of Medicine, Washington, DC) and Web of Science (Thompson Reuters, New York, New York) were used.

CONCLUSIONS

Evidence-based pathology provides methodology to evaluate the quality of information published in pathology journals and apply it to the diagnosis of tissue samples and other tests from individual patients. Information is gathered through the use of systematic reviews, using a method that is less biased and more comprehensive than ad hoc literature searches. Published data are classified into evidence levels to provide readers with a quick impression about the quality and probable clinical validity of available information. Best available evidence is combined with personal experience for the formulation of evidence-based, rather than opinion-based, guidelines that address specific practice needs.

Diagnostic significance of cell kinetic parameters in World Health Organization type A and B3 thymomas and thymic carcinomas

The prognostic importance of histologic classifications of thymic epithelial neoplasms is controversial. Evidence suggests that difficulties in reproducibility affect prognostic studies. Two thoracic pathologists independently classified 80 cases of type A or B3 thymoma and thymic carcinoma according to World Health Organization (WHO) classification. Ki-67 labeling index (LI) was used to identify cutoff points between WHO types. Recursive partitioning (Rpart) and ad hoc methods separated the data points. The pathologists agreed on type A (n = 31), type B3 (n = 21), and thymic carcinoma (n = 14). Ki-67 LI differed between types A and B3 (P < .001) and between thymic carcinoma and type A (P < .001) or type B3 (P = .001). Mitotic activity differed between thymic carcinoma and type A (P < .001) or type B3 (P < .001). Rpart revealed Ki-67 LI greater than 14.0% only in thymic carcinoma; cases with Ki-67 LI less than 5.1% did not represent thymic carcinoma. Ad hoc analysis showed Ki-67 LI greater than or equal to 13.5% represents thymic carcinoma; only type A had Ki-67 LI less than 2%. The pathologists disagreed on histologic type in 14 cases. In 11 of 14 cases with available Ki-67, the Rpart method predicted the WHO type; in 7 of 14 cases, the ad hoc method predicted the WHO type. In conclusion, Ki-67 LI is helpful in differentiating thymic epithelial neoplasms, with Ki-67 LI less than 2% and greater than or equal to 13.5% distinguishing type A thymoma and thymic carcinoma, respectively.

Is (18)F-FDG PET useful in predicting the WHO grade of malignancy in thymic epithelial tumors? A meta-analysis

AIM

To perform a systematic review and meta-analysis of published data on the role of fluorine-18-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) in predicting the WHO grade of malignancy in thymic epithelial tumors (TETs).

METHODS

A comprehensive literature search of studies published up to March 2014 was performed. Data on maximum standardized uptake value (SUVmax) in patients with low-risk thymomas (A, AB, B1), high-risk thymomas (B2, B3) and thymic carcinomas (C) according to the WHO classification were collected when reported by the retrieved articles. The comparison of mean SUVmax between low-risk thymomas, high-risk thymomas and thymic carcinomas was expressed as weighted mean difference (WMD) and a pooled WMD was calculated including 95% confidence interval (95%CI).

RESULTS

Eleven studies were selected for the meta-analysis. The pooled WMD of SUVmax between high-risk and low-risk thymomas was 1.2 (95%CI: 0.4-2.0). The pooled WMD of SUVmax between thymic carcinomas and low-risk thymomas was 4.8 (95%CI: 3.4-6.1). Finally, the pooled WMD of SUVmax between thymic carcinomas and high-risk thymomas was 3.5 (95%CI: 2.7-4.3).

CONCLUSIONS

(18)F-FDG PET may predict the WHO grade of malignancy in TETs. In particular, we demonstrated a statistically significant difference of SUVmax between the different TETs (low-grade thymomas, high-grade thymomas and thymic carcinomas).

Outcome in excised thymomas: role of prognostic factors and impact of additional malignancies on survival

Background and aims:

Although the management of thymomas has been extensively evaluated, the value of prognostic factors in the outcome of these patients remains unclear.

Methods and results:

The medical records of all patients who underwent resection of thymoma between January 1985 and September 2010 at a single thoracic unit were reviewed. Patients were followed up with reference to disease recurrence and development of additional malignancies (AM). Total thymectomy was performed in all 68 cases. Mean follow-up time was four years. Mean survival was 63.9 months. Mean disease-free interval was 13 months. Factors affecting prognosis were Masaoka staging and WHO histological sub-type. Patients with thymomas had a higher risk of developing AM when compared with a control population of individuals with other tumours ( p = 0.0002). Among thymomas, the cortical subtype was associated with a higher risk of AM ( p = 0.047) and mortality ( p = 0.001).

Conclusions:

This data confirms that Masaoka staging and WHO histologic sub-type are the most important prognostic factors in patients with thymoma. Moreover, thymomas predominantly arising from the thymic cortex are associated with a higher risk of developing other malignancies and with poorer survival. The cortical origin of thymoma could therefore be considered as a significant prognostic factor.

Anti-Apoptotic Signature in Thymic Squamous Cell Carcinomas - Functional Relevance of Anti-Apoptotic BIRC3 Expression in the Thymic Carcinoma Cell Line 1889c

The molecular pathogenesis of thymomas and thymic carcinomas (TCs) is poorly understood and results of adjuvant therapy are unsatisfactory in case of metastatic disease and tumor recurrence. For these clinical settings, novel therapeutic strategies are urgently needed. Recently, limited sequencing efforts revealed that a broad spectrum of genes that play key roles in various common cancers are rarely affected in thymomas and TCs, suggesting that other oncogenic principles might be important. This made us re-analyze historic expression data obtained in a spectrum of thymomas and thymic squamous cell carcinomas (TSCCs) with a custom-made cDNA microarray. By cluster analysis, different anti-apoptotic signatures were detected in type B3 thymoma and TSCC, including overexpression of BIRC3 in TSCCs. This was confirmed by qRT-PCR in the original and an independent validation set of tumors. In contrast to several other cancer cell lines, the BIRC3-positive TSCC cell line, 1889c showed spontaneous apoptosis after BIRC3 knock-down. Targeting apoptosis genes is worth testing as therapeutic principle in TSCC.

Thymic neoplasms: an update on the use of chemotherapy and new targeted therapies. A literature review

Thymic malignancies represent a wide range of clinical, histological and molecular entities, with probably considerable heterogeneity even among tumors of the same histotype. Systemic chemotherapy with cisplatin-based regimens continues to represent the standard of care in metastatic or inoperable refractory/recurrent diseases and ADOC regimen (including cisplatin, doxorubicin, vincristine and cyclophosphamide) demonstrated the longer overall response rate and median survival in the first line setting, although no randomized trial is available; and there is still a lack of standard treatment after first-line failure. To date research efforts are focused on translational studies on molecular pathways involved in thymic tumors carcinogenesis, aimed to better understand and predict the efficacy of chemotherapy and targeted therapy. Recent molecular characterization includes identification of a number of oncogenes, tumor suppressor genes, chromosomal aberrations, angiogenic factors, and tumor invasion factors involved in cellular survival and proliferation and in tumor growth. The use of biologic drugs is currently not recommended in a routine practice because there are limited data on their therapeutic role in thymic epitelial tumors. Because of the lack of data from adequate-sized, prospective trials are required for validation and the enrolment of patients with advanced disease into available clinical trials has to be encouraged.

Reproducibility of the WHO classification of thymomas: practical implications

BACKGROUND

The WHO-classification was shown to be an independent prognostic marker in some but not all retrospective studies possibly due to lack of reproducibility. We investigated the reproducibility of the WHO-classification and its prognostic implication using a large series of resected thymomas.

METHODS

Four independent pathologists histologically classified a surgical series of 129 thymic tumors in a blinded fashion. Fleiss' kappa-coefficient was used to assess the pathologists' overall agreement, and Cohen-Kappa to assess the agreement between two observers. Disease-related-survival (DRS) and progression-free-survival (PFS) curves were generated by Kaplan-Meier method and compared by log-rank test.

RESULTS

In 63/129 (48.8%) cases there was a complete agreement; in 43/129 (33.3%) cases 3/4 pathological diagnoses were identical; in 15/129 (11.6%) cases the diagnoses were identical by pair; in 8/129 (6.2%) cases three different pathological diagnoses were on record. The Kappa-correlation coefficient was only moderate (0.53). A following web review carried out on the 23 cases with at least two different diagnoses reached a complete consensus. The histotype showed a statistically significant impact on PFS and DRS in the classification provided by only two pathologists.

CONCLUSIONS

In this study, the agreement on WHO classification of thymomas was only moderate and this impacted on patients management. Web consensus conference on the diagnosis, more stringent diagnostic criteria or the adoption of referral diagnostic centres may substantially reduce discrepancies.

Long-term survival in thymic epithelial tumors: a single-center experience from China

BACKGROUND

To evaluate long-term survival in thymic epithelial tumors (TETs), we present our experiences at a single institution in China.

METHODS

We performed a retrospective analysis including 115 patients with TETs from 2001 to 2006. Histological diagnosis was completed based on the new WHO classification system. A univariate and multivariate survival analysis was performed, which included myasthenia gravis (MG), WHO histological type, Masaoka stage, completeness of resection, and adjuvant radiotherapy (RT).

RESULTS

WHO histological subtype was closely correlated with that of Masaoka stage. The overall median survival time was 84.4 months and the 7-year survival rate was 78%. In the univariate analysis, three prognostic factors, including WHO histology type, Masaoka stage and complete resection, were statistically significant. In the analysis of the cases with complete resection, adjuvant RT did not show obvious survival benefit. In the multivariate analysis, Masaoka stage was the only independent factor that predicted long-time survival.

CONCLUSIONS

Thymic carcinoma should be regarded as a different category of the disease due to its aggressive and poorer prognosis. Complete resection of the tumor and Masaoka stage I and II were found to contribute to a better survival. Adjuvant RT is not recommended for patients with complete resection in thymomas.

Entire hemithorax irradiation for Masaoka stage IVa thymomas

Thymomas are rare neoplasms that have an indolent growth with a preferentially intra-thoracic dissemination pattern. Surgery is currently the standard treatment of thymomas; however radiotherapy is often used in an adjuvant setting due to a high sensitivity of these tumors to such treatment. Postoperative entire hemithoracic irradiation has been used in selected Masaoka stage IVa cases after complete surgical excision of metastatic lesions. In the present article, the authors report three cases of Masaoka stage IVa thymoma that underwent entire hemithorax irradiation after surgical excision of metastatic lesions. The first two patients presented as stage IVa thymomas. The third case consisted of a pleural recurrence of a thymoma. Hemithoracic irradiation with low doses has been used by different authors; the available data shows that it is a well-tolerated treatment that could potentially lead to better loco-regional control and increased overall survival.

Thymoma and myasthenia gravis: clinical aspects and prognosis

Myasthenia gravis is present in a significant proportion of patients with thymoma. We investigated particular features of the clinical behavior of thymoma and its relationship to myasthenia in a retrospective study of 79 patients who underwent thymectomy for thymoma during the last 20 years. The presence of myasthenia gravis, Masaoka stage, World Health Organization histotype, myasthenia response, and survival were analyzed. The mean age of the patients was 56.1 ± 12.4 years, and 39 had myasthenia gravis. A significantly higher proportion of patients with myasthenia was found in B2 and B3 histotypes compared to A, AB, and B1. Among myasthenic patients, 33.3% had no response, 50% had a partial response, and 16.7% achieved complete remission. During the follow-up period, 16 (21.1%) patients died. Mean survival was 4.8 ± 1.4 years for patients with no myasthenia response, whereas those with a partial or complete myasthenia response had significantly better survival.

Thymomas II: a clinicopathologic correlation of 250 cases with a proposed staging system with emphasis on pathologic assessment

We present 250 cases of thymomas with emphasis on their clinical staging and follow-up. The patients were 120 males and 130 females between the ages of 13 and 92 years. Surgical resection was performed and histopathologic material evaluated in every case. Grossly, the tumors resected varied in size from 3 to 20 cm in greatest diameter. According to our proposed staging system, 31 cases were stage 0, 128 were stage I, 70 stage II, and 21 stage III at the time of resection. Histologically, approximately 53% of thymomas were of mixed histologic types. Follow-up information ranging from 1 to 16 years was obtained, showing significant statistical P values of .044 and .016 for overall and recurrence-free survival, respectively. We consider that our proposed staging system offers better stratification of cases and improved histologic definitions for proper staging of cases of thymoma.

Evidence-Based Principles in Pathology: Existing Problem Areas and the Development of “Quality” Practice Patterns

Context.—Contrary to the intuitive impressions of many pathologists, several areas exist in laboratory medicine where evidence-based medicine (EBM) principles are not applied. These include aspects of both anatomic and clinical pathology. Some non-EBM practices are perpetuated by clinical “consumers” of laboratory services because of inadequate education, habit, or overreliance on empirical factors. Other faulty procedures are driven by pathologists themselves.

Objectives.—To consider (1) several selected problem areas representing non-EBM practices in laboratory medicine; such examples include ideas and techniques that concern metastatic malignancies, “targeted” oncologic therapy, general laboratory testing and data utilization, evaluation of selected coagulation defects, administration of blood products, and analysis of hepatic iron-overload syndromes; and (2) EBM principles as methods for remediation of deficiencies in hospital pathology, and implements for the construction of “quality” practices in our specialty.

Data Sources.—Current English literature relating to evidence-based principles in pathology and laboratory medicine, as well as the authors' experience.

Conclusions.—Evidence-based medicine holds the promise of optimizing laboratory services to produce “quality” practices in pathology. It will also be a key to restraining the overall cost of health care.

Fascin expression in dendritic cells and tumor epithelium in thymoma and thymic carcinoma

The majority of thymomas are histologically characterized by tumor-infiltrating lymphocytes. Mature dendritic cells (DCs) are known to assemble lymphocytes through antigen presentation to T lymphocytes. Fascin, a 55-kDa actin-binding protein and a known marker for mature DCs, regulates filaments necessary for the formation of filopodia in cell migration. Moreover, fascin expression in various epithelial neoplasms has recently been reported to be associated with invasion of tumor cells and clinically aggressive manifestations. In the present study, we investigated fascin expression immunohistochemically in tissues of thymomas and thymic carcinomas surgically resected at our institute. A total of 34 thymomas and 5 thymic carcinomas were included. The amount and immunohistochemical intensity of both fascin(+) DCs and tumor epithelium were counted and assessed, and the clinicopathological data were also scored. Statistical analyses revealed that the amount of fascin(+) DCs with the formation of clusters was associated with lymphocyte-rich variants (p=0.002) and cortical differentiation (p=0.037) of thymoma with complication from myasthenia gravis (p=0.002). The quantity of fascin(+) epithelium was associated with a strong intensity of fascin in infiltrating DCs (p=0.002) with the formation of clusters (p=0.002) and favorable prognosis, as assessed by the Masaoka staging system (p=0.001). The amount of infiltrating DCs (p=0.024) and fascin(+) epithelium were lower in thymic carcinoma. It was concluded that fascin(+) epithelium may induce tumor immunity through the surveillance activity of fascin(+) DCs in thymic neoplasms, thus improving prognosis.