Extrathoracic metastases of thymic origin: a review of 35 cases

Abstract

Thymic tumors are categorized as types A, AB, B1, B2, B3, and thymic carcinoma under the World Health Organization (WHO) classification. Thymomas are typically slow growing tumors that predominantly involve the surrounding structures through direct invasion, while thymic carcinomas tend to be more aggressive. A significant number of patients are asymptomatic and can present with metastases as the first presentation. The exact incidence of extrathoracic metastases from thymoma is not known. This study describes a series of 35 cases of histologically documented metastatic thymomas and thymic carcinomas at extrathoracic sites. These cases were classified according to the current World Health Organization (WHO) classification criteria, and we present their clinical data as well as discuss the differential diagnoses of these lesions. Our study shows that all types of thymic tumors, regardless of histologic type, can be associated with invasion and metastases to thoracic and extrathoracic sites. It is the most aggressive variant invading surrounding structures with metastases, 2 although embolic metastases of thymic carcinoma leading to extrathoracic metastases are very rare. 4 Since, thymic cancers invade locally, diagnoses of metastases are difficult. Locally advanced thymic tumors often present as pleural plaques, which can be misdiagnosed as lung metastases on imaging studies. Thus, it becomes very important to appropriately define metastases in these tumors. For this reason, we defined only lesions outside the thorax that were histologically similar to the primary thymic tumors as metastases.Although the exact incidence of extrathoracic metastases from thymoma is not known, in 1983, Ichino et al 5 documented 83 cases in the literature. However, most of the metastatic sites were not biopsied and histology was not available. In addition, the older literature does not make a distinction between epithelial lesions (true thymic tumors) and other neoplasms arising in the region of thymus. In any event, these studies suggest liver, bone, and lymph nodes as common sites of extrathoracic metastases of malignant thymoma. [4][5][6] Moreover,

The role of histology in predicting recurrence of type A thymomas: a clinicopathologic correlation of 23 cases

“…Several studies have documented invasive growth and even metastases in tumors of this subtype. [4][5][6] This realization has prompted a closer look at the morphological features that could be associated with adverse outcomes. Nonaka and Rosai 7 published a series of 13 cases of type A thymomas showing atypical features.…”

“…[1][2][3] However, recent studies, by us amongst others, have challenged this concept. 4,5 Types A and AB tumors have been documented to have aggressive potential and the capability of spreading in or outside of the thoracic cavity. 4,6 The recognition that some spindle cell thymomas might behave in an aggressive manner has led to a re-examination of the features seen in these tumors.…”

The prognostic value of architectural patterns in a study of 37 type AB thymomas

“…However, recent data presented by us and among others have documented recurrences and metastases in both type A and type AB thymomas. [4][5][6] More recently, Nonaka and Rosai 7 have published a series of cases of type A thymomas with distinct atypia (atypical type A thymomas). Some of these cases had aggressive outcomes.…”

Establishment and characterization of a novel cell line derived from human thymoma AB tumor

“…3 Although complete resection and chemotherapy are effective therapies for early disease, metastases remain a challenge. [4][5][6] Tumors of all histological types, albeit with different frequencies, can spread locally within the pleura and pericardial cavity, and give rise to local or distant metastases. 5,6 The treatment strategies include the combination of surgery, radiation and chemotherapy based on the extent of the disease and the status of tumor resectability.…”

“…[4][5][6] Tumors of all histological types, albeit with different frequencies, can spread locally within the pleura and pericardial cavity, and give rise to local or distant metastases. 5,6 The treatment strategies include the combination of surgery, radiation and chemotherapy based on the extent of the disease and the status of tumor resectability. 3,4 Surgery is the main choice of treatment for localized thymic tumors, as complete resection is the most significant prognostic factor.…”