WHO types A and AB thymomas: not always benign

Jain, Rohit; Mehta, Rutika; Henley, John; Kesler, Kenneth A.; Loehrer, Patrick J.; Badve, Sunil

doi:10.1038/modpathol.2010.172

Cited by 46 publications

(58 citation statements)

References 53 publications

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“…8 However, we have previously reported a large series of cases of type A tumors associated with aggressive intrathoracic disease. 16 This has been more recently confirmed by Moran et al 17 In this light, it is important to note that brain metastasis has been reported 18 in a patient with type A thymoma, which was histologically confirmed by Dr Rosai. In addition, the 10-year survival rates in patients with completely excised tumors and/or type A tumors have not always been 100%.…”

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confidence: 69%

Extrathoracic metastases of thymic origin: a review of 35 cases

et al. 2012

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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,

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Section: Discussionmentioning

confidence: 69%

Extrathoracic metastases of thymic origin: a review of 35 cases

et al. 2012

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“…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.…”

Section: Discussionmentioning

confidence: 99%

“…[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.…”

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confidence: 99%

“…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. More recently, a concept of 'atypical spindle cell/ type A tumors' has been put forth by Nonaka and Rosai.…”

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

et al. 2013

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Spindle cell thymomas (type A), as per the WHO definition, are benign tumors with an excellent prognosis. However, recent studies document aggressive behavior with local recurrences as well as extrathoracic metastases. More recently, Nonaka and Rosai have raised the question as to whether atypical features like cellular atypia, mitotic activity, necrosis, and vascular permeation could predict the adverse outcomes of these tumors. In an effort to address the 'atypia and outcome' issue of spindle cell thymomas, we analyzed our database of over 600 cases of thymic tumors to identify type A thymomas. The presence of histomorphological features like tumor size, nuclear shape and variability, mitotic rate, and presence/absence of necrosis were correlated with Masaoka stage, relapse/recurrence, and extrathoracic metastases. The study identified 23 patients of pure spindle cell thymomas (WHO type A) ranging in age from 40 to 88 years (median age, 54 years) and with male-to-female ratio of 1:0.9. Approximately 43% of the cases had recurrence or metastases during the followup period (average, 49 months). The presence of necrosis correlates with both relapse and extrathoracic metastases but not with the stage of diagnosis. However, none of the other clinical or histological features, including size, predominant nuclear shape, nuclear variability, and mitotic activity, were correlated with the outcome parameters, such as stage at diagnosis, presence or absence of relapse, and extrathoracic metastases. Histological atypia is fairly common in WHO type A thymomas. The presence of necrosis was associated with both locoregional and systemic disease. However, none of the other clinical or histological features correlated with aggressive behavior.

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“…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.…”

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

et al. 2014

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Spindle cell thymomas with prominent amount of lymphocytes are classified as WHO type AB tumors. However, there are architectural pattern differences in these tumors. We investigated the importance of architectural pattern in type AB thymomas in relation to prognostic value. Archival hematoxylin-eosin stained slides of 37 AB type thymomas were reviewed for the presence (type 1) or absence (type 2) of reticular growth pattern. Reticular growth pattern is defined as the presence of a network of elongated bland spindle cells separating nests of tumor cells admixed with lymphoid cells. The architectural patterns were correlated with tumor stage at diagnosis and presence or absence of recurrent disease. The analysis identified 18 cases of type 1 AB thymoma and 19 cases of type 2. Type 2 cases also had greater cytologic atypia within the spindle cells. Patients with type 1 tumors were more likely to have early stage disease. In contrast, type 2 pattern was associated with higher stage at diagnosis (Po0.001) and greater likelihood for recurrence (Po0.05) and metastases. Architectural features are prognostically relevant in classification of WHO AB type thymomas and may constitute a form of personalized medicine. Independent confirmation of the findings is necessary to confirm the association of architectural pattern with outcomes.

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WHO types A and AB thymomas: not always benign

Cited by 46 publications

References 53 publications

Extrathoracic metastases of thymic origin: a review of 35 cases

Extrathoracic metastases of thymic origin: a review of 35 cases

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

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

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