Importance of Lymph Node Dissection in Thymic Carcinoma

Difficult Decisions in Minimally Invasive Surgery of the Thymus

A minimally invasive resection of thymomas has been accepted as standard of care in the last decade for early stage thymomas. This is somewhat controversial in terms of higher-staged thymomas and myasthenia gravis patients due to the prognostic importance of complete resections and the indolent characteristics of the disease process. Despite concerted efforts to standardize minimally invasive approaches, there is still controversy as to the extent of excision, approach of surgery, and the platform utilized. In this article, we aim to provide our surgical perspective of thymic resection and a review of the existing literature.

Lymph Nodes Involvement and Lymphadenectomy in Thymic Tumors: Tentative Answers for Unsolved Questions

Simple Summary

The standard treatment for thymic tumors is radical thymectomy with en bloc resection of the surrounding tissue for early stages, while multimodality therapy has to be considered in the advanced stages. Due to the rarity of nodal metastases in thymic tumors, little attention has been paid to their incidence, pattern and prognostic significance and, consequently, no standard nodal mapping or consensus on lymph node dissection has currently been established. Moreover, no data indicate which subgroup of patients would be appropriate candidates for lymph node dissection D or the extent to which lymph nodes should be harvested. The aim of this review is to collect evidence from the useful literature to help physicians in designing the best surgical procedure when dealing with thymic malignancies and to plan the best multidisciplinary strategy in case of advanced stage thymic tumors.

Abstract

Thymic tumors are the most common primary neoplasms of the anterior mediastinum, although, when compared with the entire thoracic malignancies, they are still rare. Few studies addressed the questions about lymph node involvement pattern in thymic neoplasms, about which subgroup of patients would be appropriate candidates for lymph node dissection or about the extent of lymphadenectomy or which lymph nodes should be harvested. The aim of this review is to collect evidence from the literature to help physicians in designing the best surgical procedure when dealing with thymic malignancies. A literature review was performed through PubMed and Scopus in May 2021 to identify any study published in the last 20 years evaluating the frequency and the extent of lymph node dissection for thymic tumors, its impact on prognosis and on postoperative management. Fifteen studies met the inclusion criteria and were included in this review, with a total of 9452 patients with thymic cancers; lymph node metastases were found in 976 (10.3%) patients in total. The current literature is heterogeneous in the classification and reporting of lymph node metastases in thymic carcinoma, and data are hardly comparable. Surgical treatment should be guided by the few literature-based pieces of evidence and by the experience of the physicians.

Lymph node dissection in thymic carcinomas and neuroendocrine carcinomas

OBJECTIVES

Although lymph node (LN) metastases are not uncommon in thymic carcinomas, preoperative LN evaluation, intraoperative lymph node dissection (LND) and postoperative outcomes remain unknown. The aim of this study was to elucidate the characteristics of and outcomes in patients with thymic carcinomas and thymic neuroendocrine carcinomas undergoing LND.

METHODS

A retrospective chart review was performed using our multi-institutional database to identify patients who underwent resection and LND for thymic carcinoma or thymic neuroendocrine carcinoma between 1991 and 2018. An enlarged mediastinal LN was defined as having a short-axis diameter >1 cm. We assessed survival outcomes using the Kaplan-Meier analysis.

RESULTS

N1-level LND was performed in 41 patients (54.6%), N2-level LND in 14 patients (18.7%) and both-level LND in 16 patients (21.3%). Pathological LN metastasis was detected in 20 patients (26.7%) among the 75 patients undergoing LND. There was a significant difference in the number of LN stations (P = 0.015) and metastasis factor (P = 0.0042) between pathologically LN-positive and pathologically LN-negative patients. The sensitivity of enlarged LNs on preoperative computed tomography was 18.2%. There was a tendency towards worse overall survival of pathologically N2-positive patients, although the difference was not statistically significant (P = 0.15).

CONCLUSIONS

Preoperative CT appears to play a limited role in detecting pathological LN metastases. Our findings suggest that the significance of N1- and N2-level LND should be evaluated in prospective studies to optimize the postoperative management of patients with thymic carcinomas and neuroendocrine carcinomas.

Effect of Lymph Node Dissection on the Prognosis of Thymic Carcinomas and Thymic Neuroendocrine Tumors

We aimed to analyze the effect of lymph node dissection (LND) and accurate lymph node (LN) status on the survival and prognosis of patients with thymic carcinomas (TCs) and thymic neuroendocrine tumors (TNETs) undergoing surgical treatment. The Surveillance, Epidemiology, and End Results database was queried for patients who underwent surgical resection for TCs and TNETs during 1998-2016. LN status were defined as no LND (LND-), pathologically negative with LND (N0), and LN metastasis positive (N+). We investigated outcomes of LN status together with other clinicopathological features for overall survival (OS). Subgroup analyses were performed between LND-, N0, and N+ cohorts using propensity score matching, to analyze the significance of LND in prognosis. A total of 812 patients were enrolled, including 623 with TCs and 189 with TNETs. The proportion of LN metastasis positive in TNETs was 58.8% which was significantly higher than that in TCs (30%) (P < 0.001). In multivariable Cox analysis of OS, patients with LND- had a significantly worse prognosis than those with N0 (P = 0.018); there was no difference between N+ and LND- (P = 0.560). After propensity score matching, patients with N0 still had better survival than those with LND- and N+ in subgroup univariable and multivariable analyses of OS; however, the survival of patients with LND- and N+ was not significantly different in multivariable analysis. It was demonstrated that LND in TCs and TNETs can clarify the status of LN metastasis, to more accurately evaluate patients' long-term prognosis.

The treatment and survival of patients with postoperative recurrent thymic carcinoma and neuroendocrine carcinoma: a multicenter retrospective study

PURPOSE

There are few data available on the outcomes of postoperative recurrent thymic carcinoma (TC) and thymic neuroendocrine carcinoma (TNEC). The aim of this study is to evaluate the treatment and survival in patients with recurrent TC and TNEC after undergoing surgical resection.

METHODS

A retrospective chart review was performed using our multicenter database to identify patients with a postoperative recurrence of TC and TNEC from 1995 to 2018. The clinicopathological factors were reviewed and the survival outcomes were analyzed.

RESULTS

Sixty patients were identified among 152 patients who underwent resection of TC and TNEC. The median follow-up period from the first recurrence was 14.8 months (range 0-144). The 5-year post-recurrence survival was 23% for the whole cohort. According to a univariable analysis, advanced stage [hazard ratio (HR) 2.81, 95% confidence interval (CI) 1.09-9.54], interval between primary surgery and recurrence (HR 0.97, 95% CI 0.95-0.99), any treatment for recurrence (HR: 0.27, 95% CI 0.13-0.58) and chemotherapy for recurrence (HR: 0.46, 95% CI 0.22-0.95) were significant factors related to post-recurrence survival.

CONCLUSIONS

Chemotherapy rather than surgery appears to be the mainstay treatment for managing patients with postoperative recurrent TC and TNEC and it may also be considered in multidisciplinary management. Further studies with a larger sample size are required to confirm our findings.

Robotic thymectomy for advanced thymic epithelial tumor: indications and technical aspects

Robotic thymectomy is widely accepted as a valuable treatment option for surgical resection of thymic epithelial tumor as minimally invasive surgery has shown better early clinical outcomes than open surgery. Technical advances in robotic surgery have expanded the indications for robotic thymectomy, and the technique can be used to perform complete resection of advanced thymic epithelial tumor requiring concomitant resection of adjacent structures. To ensure complete resection, a multi-disciplinary approach, with thorough preoperative evaluation, must be adopted to determine whether a patient shows surgical indications for advanced thymic epithelial tumor. The early clinical outcomes after robotic thymectomy to treat advanced thymic epithelial tumor are promising; however, the long-term oncologic outcomes should be evaluated in the further studies.

Laparoscopic dissection for pelvic lymph node recurrence of thymic carcinoma: A case report

Thymic carcinoma, a rare mediastinal neoplasm, is characterized by extensive local invasion and distant metastasis. To our knowledge, this is the first case report demonstrating the efficacy of laparoscopic dissection for pelvic lymph node metastases from thymic carcinoma. A 64-year-old man was found to have a mediastinal mass by CT and underwent radical resection. Six months after resection of his thymic carcinoma, follow-up CT revealed a gluteal tumor and enlarged pelvic lymph nodes. The gluteal tumor was resected percutaneously. Two months after this procedure, PET showed that the three pelvic lymph nodes had abnormal uptake of ¹⁸ F-fluorodeoxyglucose and had enlarged further. The patient accordingly underwent laparoscopic dissection of these lymph nodes. Pathological examination of all resected specimens showed metastatic thymic carcinoma. We recommend laparoscopic dissection of pelvic lymph node metastases because it provides a clear intraoperative view and is minimally invasive.

Effect of clinicopathologic features on survival of patients with thymic carcinomas and thymic neuroendocrine tumors: A population-based analysis

BACKGROUND

Thymic carcinomas (TCs) and thymic neuroendocrine tumors (TNETs) are aggressive cancers with poor survival outcome and limited investigation. This study is to investigate clinicopathologic features on TC and TNET patients' prognosis of a large cohort.

MATERIALS AND METHODS

The Surveillance, Epidemiology, and End Results database were used to identify a total of 362 TC and TNET patients with documented clinicopathologic features we investigated. The characteristics and overall survival of the TC and TNET patients were studied.

RESULTS

Two hundred and forty TC and 122 TNET patients were identified. For the entire cohort of TC and TNET, histologic type (P < 0.001), tumor size (P = 0.015), Masaoka-Koga stage (P = 0.008), regional node positive (P = 0.004), surgery of primary site (P < 0.001), lymph node surgery (P = 0.013), and chemotherapy (P = 0.001) were considered as significant clinicopathologic features that could affect prognosis of TC and TNET patients in univariate analysis. More importantly, histologic type (P < 0.001), regional nodes positive (P = 0.03) and surgery of primary site (P < 0.001) were able to independently predict overall survival of those patients. In addition, for the cohort of TC, we found that regional nodes positive (P = 0.034) and surgery of primary site (P = 0.001) could be independent predictors of TC patients' survival.

CONCLUSION

Regional nodes detection is essential for TC and TNET patients. Surgery of primary site is the preferred primary treatment for those patients.

A Nomogram Predicting Recurrence and Guiding Adjuvant Radiation for Thymic Carcinoma After Resection

BACKGROUND

Resection is an effective treatment for thymic carcinoma. We aimed to develop a nomogram for postoperative prediction of recurrence-free survival for patients with thymic carcinoma and guide adjuvant radiotherapy.

METHODS

A total of 198 patients who underwent surgery were divided into training cohort (n = 152) and validation cohort (n = 46). Clinicopathologic features and independent factors for postoperative recurrence were analyzed. A predictive nomogram was developed based on the prognostic factors. Discrimination and predictive accuracy of the model were measured using the concordance index (C-index), calibration curves, and validation study.

RESULTS

The overall 1-, 3-, and 5-year recurrence rate of 198 patients was 7.6%, 27.9%, and 39.9%, respectively. Independent predictors of recurrence-free survival on multivariate analysis were incorporated into the nomogram. Calibration curves for the probability of 1-, 3-, and 5-year recurrence-free survival fitted well. The C-index of the nomogram for predicting recurrence-free survival was 0.862 (95% confidence interval: 0.804 to 0.919). Internal validation supported the results optimally. Adjuvant radiotherapy was effective for patients with a total score greater than 208.

CONCLUSIONS

Our nomogram for predicting recurrence-free survival had good performance. Adjuvant radiotherapy should be recommended for patients with a total score greater than 208.

IASLC/ITMIG Staging System and Lymph Node Map for Thymic Epithelial Neoplasms

Thymic epithelial neoplasms are rare malignancies that arise from the thymus and include thymoma, thymic carcinoma, and thymic neuroendocrine tumors. At least 15 different stage classifications have been proposed for thymic epithelial neoplasms and used to varying degrees in clinical practice, many of which have been constructed from small groups of patients. Traditionally, the Masaoka and Masaoka-Koga staging systems have been the schemes most commonly employed, and the latter has been recommended for use by the International Thymic Malignancy Interest Group (ITMIG). An official, consistent stage classification system has recently been recognized by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC), which are responsible for defining stage classifications for neoplasms. To establish this stage classification system, the International Association for the Study of Lung Cancer (IASLC) and ITMIG amassed a large retrospective database and evaluated this group of cases to develop proposals for the eighth edition of the stage classification manuals. For this endeavor, IASLC provided funding and statistical analysis and ITMIG provided the involvement of the clinicians and researchers actively participating in the study of thymic epithelial neoplasms. To accomplish this, a Thymic Domain of the Staging and Prognostic Factors Committee (TD-SPFC) was established to formulate the rationale, methodology, and definitions of this tumor-node-metastasis (TNM) staging system, which is presented in this article. ^© RSNA, 2017.

Stage IVb thymic carcinoma: patients with lymph node metastases have better prognoses than those with hematogenous metastases

Background

This study aimed to analyze the pattern of lymphogenous and hematogenous metastases in patients with stage IVb thymic carcinomas and identify prognostic factors for their survivals.

Methods

Between September 1978 and October 2014, 68 patients with pathologically confirmed stage IVb thymic carcinomas were treated at Fudan University Shanghai Cancer Center. Forty-three patients had lymph node involvement without distant metastases, and the remaining 25 patients had hematogenous metastases. Clinical-pathological characteristics, including age, sex, histologic subtype, tumor size, metastasis, treatment modalities, such as surgical resection, radiotherapy, and chemotherapy, and clinical outcomes, such as overall survival (OS) and progression free survival (PFS), were analyzed.

Results

The median follow-up time was 22 months (range, 1–126 months). The median OS of all patients with stage IVb thymic carcinomas was 30 months, and the 5-year overall survival rate was 25.1%. The median PFS was 11 months, and the 5-year PFS was 17.9%. Stage IVb patients with lymph node involvement had a better survival than those with distant metastasis (40 vs. 20 months, p = 0.002). Patients with myasthenia gravis had a worse prognosis (p = 0.033). Multivariate analysis identified metastatic status as an independent prognostic factor for OS in patients with stage IVb thymic carcinomas.

Conclusions

Patients with lymph node involvement had a better survival than those with distant metastases. Much work remains to investigate the prognosis of patients with stage IVb thymic carcinomas and to explore different treatment strategies for patients with lymph node involvement and distant metastases.

Lymph Node Dissection in Thymic Malignancies: Implication of the ITMIG Lymph Node Map, TNM Stage Classification, and Recommendations

OBJECTIVES

The aim of this study is to investigate the pattern of lymphatic metastasis and suggest a lymph node dissection (LND) strategy for thymic malignancies.

METHODS

We retrospectively reviewed 131 thymic malignancy patients who had undergone LND. The recently introduced nodal map of the International Thymic Malignancy Interest Group/International Association for the Study of Lung Cancer and the TNM (tumor, node, metastasis) stage classification were used for grouping and staging the lymph nodes. The pattern of lymphatic metastasis and factors in lymphatic metastasis were investigated.

RESULTS

Node metastasis was detected in 13 patients (N1 in six and N2 in seven). Six N2 patients (86%) had right paratracheal node (RPN) metastases. The rates of node metastasis were 1% at T1 and 37.5% at T2/3 (p < 0.001). The rates of node metastasis were 8% in the M0 and 43% in the M1 (p = 0.03). The rate was higher for thymic carcinoma (25%) than for thymoma (5.1%, p = 0.01), and the rates also differed between the subtypes of thymoma. There was no node metastasis of the A, AB, or B1 types. Tumor size was also a significant factor in node metastasis. The optimal cutoff value for the node metastasis was 6 cm and the specificity was 62%. Only 16% of the patients had received a preoperative histologic diagnosis. All patients with node metastasis had TNM stage II or higher thymic malignancy. The freedom from recurrence rate of the pN1/2 was significantly worse than that of the pN0 (5-year rate 38.5% versus 87.9%, p < 0.001).

CONCLUSION

A status of stage II or higher was the most specific predictor of node metastasis, and the RPN was a crucial station for lymphatic metastasis in thymic malignancies. Thus, LND including RPN is recommended in stage II or higher thymic malignancies.

Standardized definitions and policies of minimally invasive thymoma resection

A wide range of technical approaches for the minimally invasive resection of thymus have been described. Most of the time, the benefits are superior cosmetic outcome and shorter duration of postoperative stay. Other demonstrable differences that have been reported include shorter duration of surgery, less intraoperative blood loss and less postoperative pleural drainage. Robotic surgery and video-assisted surgery (VATS) may become routinely used procedures in the treatment of stage I and II thymomas.

Thymectomy and transpericardial nodal dissection

Neuroendocrine thymic tumors (NETTs) are rare neoplasms. Surgical resection of the tumor and the involved lymph node remains the treatment of choice. We describe the surgical technique adopted in a patient with preoperative diagnosis of thymic malignant tumor and subcarinal nodal involvement. Through a median sternotomy, an extended thymectomy was performed as a first step. Then, through the transpericardial approach (opening of the anterior and posterior pericardium and isolation of ascending aorta, superior vena cava, and main right pulmonary artery), mediastinal nodal dissection (#2R, #4R, #4L, #5 and #7) was performed. Definitive pathology showed a NETT without nodal involvement. The patient received adjuvant chemotherapy, and is alive without disease 19 months after the surgery. Complete surgical excision and adjuvant therapy appears to offer the best hope for prolonged survival for NETTs. The surgical technique should be individualized according to tumor location. Thoracic surgeons should be familiar with this technique, which provides a good technical and oncological result.

The IASLC/ITMIG Thymic Epithelial Tumors Staging Project: proposals for the N and M components for the forthcoming (8th) edition of the TNM classification of malignant tumors

Stage classification is an important underpinning of management of patients with cancer, and rests on a combination of three components: T for tumor extent, N for nodal involvement, and M for more distant metastases. This article details an initiative to develop proposals for the first official stage classification system for thymic malignancies for the 8th edition of the stage classification manuals. Specifically, the results of analysis of a large database and the considerations leading to the proposed N and M components are described. Nodal involvement is divided into an anterior (N1) and a deep (N2) category. Metastases can involve pleural or pericardial nodules (M1a) or intraparenchymal pulmonary nodules or metastases to distant sites (M1b).

The ITMIG/IASLC Thymic Epithelial Tumors Staging Project: A Proposed Lymph Node Map for Thymic Epithelial Tumors in the Forthcoming 8th Edition of the TNM Classification of Malignant Tumors

Although the presence of nodal disease is prognostic in thymic malignancy, the significance of the extent of nodal disease has yet to be defined. Lymph node dissection has not been routinely performed, and there is currently no node map defined for thymic malignancy. To establish a universal language for reporting as well as characterize the staging of this disease more accurately, an empiric node map is proposed here. This was developed using prior classification systems, series reporting specifics of nodal involvement, anatomical studies of lymphatic drainage, and preexisting node maps of the chest as defined by the International Association for the Study of Lung Cancer and the neck as defined by the American Academy of Otolaryngology-Head and Neck Surgery and the American Society for Head and Neck Surgery. The development of this node map was a joint effort by the International Thymic Malignancy Interest Group and the Thymic Domain of the IASLC Staging and Prognostic Factors Committee. It was reviewed and subsequently approved by the members of ITMIG. This map will be used as an adjunct to define node staging as part of a universal stage classification for thymic malignancy. As more data are gathered using definitions set forth by this node map, a revision may be undertaken in the future.

Thymic carcinoma patients with myasthenia gravis exhibit better prognoses

BACKGROUND

Thymic carcinoma is an aggressive mediastinal neoplasm with a poor prognosis, but the factors that contribute to its prognosis are not completely understood. Myasthenia gravis (MG) can coexist with thymic carcinoma with low incidence, but the effect MG has on thymic carcinoma prognosis is unknown. Here, we investigated the prognostic factors of thymic carcinoma and the influence of MG on patients with this disease.

METHODS

Between January 1996 and December 2012, 49 patients were diagnosed with thymic carcinoma and surgically treated at our institution. Clinical data and survival information were recorded and systematically reviewed. Kaplan-Meier survival curves were generated, and independent prognostic factors were identified by Cox's proportional hazard model.

RESULTS

Complete resection was achieved in 30 patients (61.2 %), and incomplete resection was performed on the other 19 patients (38.8 %). Six of the 49 patients with thymic carcinoma also presented with MG (12.2 %). Interestingly, these 6 patients exhibited much better prognoses when compared to the other 43 patients. Patients with MG also had significantly smaller tumors (P = 0.045), earlier Masaoka stage (P = 0.048), and higher complete resection rates (P = 0.042). However, multivariate analysis demonstrated that complete resection was the only independent predictor for overall survival (OS) (P < 0.001).

CONCLUSIONS

The OS of patients with thymic carcinoma depends on complete resection, but patients with MG also demonstrate improved prognoses. MG patients have higher rates of complete surgical resection, which may account for their better prognoses. Patients with MG have unique features that may aid in the clinical management of these patients.

Long-term follow-up and prognostic factors for advanced thymic carcinoma

The aim of this study was to evaluate the long-term survival outcomes in patients with advanced thymic carcinoma and identify prognostic factors influencing the survival. We retrospectively analyzed 90 consecutive patients with pathologically confirmed advanced thymic carcinoma (Masaoka III and IV) in our institute, from December 2000 to 2012. Age, sex, clinical characteristics, laboratory findings, Masaoka and tumor node metastasis staging, pathologic grade, and treatment modalities were analyzed to identify prognostic factors associated with the progress-free survival (PFS) and the overall survival (OS) rates. Statistical analysis was conducted using SPSS, version 19.0 (SPSS, Inc, Chicago, IL). A total of 73 (81.1%) male and 17 (18.9%) female patients participated in the study. The median follow-up time was 75 months (range, 20-158 months). The 5-year PFS and OS rates were 23.6% (95% confidence interval [CI], 14.6%-33.8%) and 35.7% (95% CI, 25.1%-46.4%), respectively. The multivariate Cox regression model analysis showed that factors improving the PFS were the normal lactate dehydrogenase (LDH) level (P<0.001), Masaoka III stage (P=0.028), and radiotherapy (RT) (P<0.001). The LDH (P<0.001), T stage (P<0.001), and the pathologic grade (P=0.047) were independently prognostic of OS. Long-term follow-up of the advanced thymic carcinoma showed poor outcomes of PFS and OS. LDH, Masaoka stage, and RT affected the PFS, and LDH, T stage, and pathologic grade seemed to affect the OS. Establishing a better staging system for predicting outcomes would be warranted.

What is the role of lymph nodal metastases and lymphadenectomy in the surgical treatment and prognosis of thymic carcinomas and carcinoids?

A best evidence topic in thoracic surgery was written according to a structured protocol. We looked at the clinical relevance of lymph node involvement and nodal (N) stage, in thymomas, thymic carcinomas and carcinoids. The possible role of lymphadenectomy in addition to thymectomy was also evaluated. A total of 605 papers were found, of which nine represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers were tabulated. In the Yamakawa-Masaoka classification, based on 226 patients, lymph nodes were classified as anterior mediastinal (N1), defined as nodes surrounding the thymus gland; intrathoracic (N2), all nodes within the thorax excluding N1; and extrathoracic nodes (N3). Kondo validated the Yamakawa-Masaoka classification in a multicentric cohort of 1320 patients. Thymomas presented nodal involvement in 1.8% of cases, carcinomas in 27% of cases, and carcinoids in 28% of cases. The role of nodal status in defining the stage was even more emphasized in the staging system developed by Tsuchiya for thymic carcinomas. In the Istituto Nazionale Tumori classification, thymomas with N1 or N2 were considered as locally advanced disease with a 95-month disease-free survival rate for locally advanced disease of 46.9 vs 98.6% for locally restricted disease (absence of nodal involvement). Weissferdt and Moran, on a series of 65 thymic carcinomas, underlined the clinical relevance of nodal involvement. Positive lymph nodes were associated with significantly worse survival (P = 0.01070). Okuma, in a series of 68 advanced stage thymic carcinomas, showed that curative-intent surgical treatment was related to prolonged survival (P = 0.03). In particular, IVb tumours due to node-only involvement had better survival when radical resection was achieved when compared with IVb due to distant metastases (P = 0.03). Sung et al. showed the importance of harvesting 10 or more lymph nodes and dissecting intrathoracic lymph nodes to ensure a more complete stadiation of thymic carcinomas. The results underline the clinical relevance and prognostic value of nodal involvement in thymic carcinomas and carcinoids. In these cases, lymphadenectomy is desirable to allow the real definition of N status.