Yasuko Hosaka

Masaoka Stage and Histologic Grade Predict Prognosis in Patients With Thymic Carcinoma

BACKGROUND Thymic carcinoma is a rare tumor. Limited data are available regarding the effectiveness of treatment and the prognosis of thymic carcinoma. The present study aimed to clarify the prognostic factors in patients who underwent resection. METHODS The study retrospectively reviewed 21 patients (15 men, 6 women) with thymic carcinoma who had undergone resection at Niigata University Hospital. RESULTS Masaoka stage was II in 4 patients, III in 9, IVa in 2, and IVb in 6. Histologic subtypes were squamous cell carcinoma in 14 patients, adenocarcinoma in 2, atypical carcinoid in 3, and undifferentiated carcinoma in 2. Histologic grade by degree of differentiation was low in 4 tumors, intermediate in 12, and high in 5. Treatment comprised resection alone in 6 patients and resection along with multimodal therapies in 15. Complete resection was achieved in 14 (67%). Eight patients died of tumor. Recurrence was documented in 7 of 14 patients with complete resection, and 5 received additional treatment. The overall 5-year survival rate was 61.1%, and the disease-free 5-year survival rate was 66.8% for the 14 with complete resection. By multivariate analysis, Masaoka stage and histologic grade were significant independent prognostic factors for overall survival. CONCLUSIONS The surgical outcome of patients with thymic carcinoma depends on the Masaoka stage and histologic grade. Patients with early Masaoka stage and low or intermediate histologic grade had favorable prognoses.

Absence of gene mutations in KIT-positive thymic epithelial tumors

BACKGROUND Overexpression of KIT, a tyrosine kinase receptor protein encoded by the proto-oncogene c-kit, is observed in human neoplasms such as gastrointestinal stromal tumors (GISTs), myeloproliferative disorders, melanoma and seminoma. In patients with GIST, overexpression of mutated KIT within the tumor is predictive of response to molecular targeted therapy using imatinib. However, the role of KIT expression in thymic carcinoma is not fully understood. METHODS Thymic epithelial tumors from 37 patients (17 thymic carcinomas and 20 thymomas) were examined. Immunohistochemical staining with anti-KIT polyclonal antibody and anti-CD5 was performed. Mutation analyses in the juxtamembrane domains, exons 9 and 11, and in the tyrosine kinase domains, exons 13 and 17, were undertaken using polymerase chain reaction (PCR) and direct DNA sequencing in KIT-positive samples. RESULTS KIT- and CD5-positive staining was observed only in thymic carcinoma. Percentage of positive staining was 100% in squamous cell carcinoma, with no positive staining in other histologies, including atypical carcinoid. Mutation analysis of the KIT gene was performed in 11 squamous cell carcinomas, 1 adenocarcinoma and 1 adenosquamous cell carcinoma. None of the tested samples showed mutations in any of the four exons. CONCLUSIONS Squamous cell carcinoma of the thymus frequently expressed KIT and CD5 proteins, whereas other tumors did not. Unlike GIST, overexpression of KIT does not necessarily indicate gene mutation in thymic carcinoma. KIT and CD5 appear useful for evaluating and subtyping thymic epithelial tumors.

Primary thymic adenocarcinoma coexisting with type AB thymoma: a rare case with long-term survival

Thymic carcinoma is a rare tumor. The most common histological subtype is squamous cell carcinoma, and only a few cases of thymic adenocarcinoma have been reported. A case of papillary adenocarcinoma of thymic origin that coexisted with type AB thymoma as a separate nodule is presented herein. The patient was found to have an abnormal mediastinal shadow on chest X-ray. A computed tomography scan revealed a round, 6.5-cm-diameter mass in the right anterior mediastinum. The preoperative diagnosis was thymoma, and thymothymectomy was performed. On pathological examination, two tumors, which were diagnosed as papillary adenocarcinoma and type AB thymoma, respectively, were present in the thymus without any connection with each other. The patient has been alive without any signs of recurrence for 11 years after surgery. We diagnosed the adenocarcinoma in this case was a primary thymic carcinoma.