Epithelioid Mesothelioma

In this article, we will discuss Epithelioid Mesothelioma (Pathology). So, let’s get started.

Epithelioid Mesothelioma (Pathology)

Solid, glandular, and/or tubulopapillary patterns were observed in the pure epithelioid mesotheliomas or the epithelioid component of the biphasic mesotheliomas. The solid pattern was composed of sheets and/or nests of polygonal to cuboidal atypical cells. This pattern was observed in 40 tumors (the epithelioid component was pure solid in 4 cases, predominantly solid in 23, and focally solid in 13). The glandular pattern was formed by tubules and glands lined by cuboidal to columnar cells Image 1 Al and Image 138 and was evident in 34 cases (pure glandular in 3 tumors, predominantly glandular in 10, and focally glandular in 21). Two of the glandular tumors also had focal areas with microcystic features composed of flattened or attenuated cell-lining glands, the so-called adenomatoid pattern. Tumors with tubulopapillary features were formed by papillary structures with fibrovascular cores lined by cuboidal to flattened cells and branching tubules lined by low cuboidal to columnar cells. These architectural features were present in 26 cases (pure tubulopapillary in 1 case, predominantly tubulopapillary in 7 cases, and focally tubulopapillary in 18).

The 3 epithelioid patterns coexisted in 12 cases (of 40 tumors with mixed epithelioid patterns). The most frequent associations between morphologic patterns in the remaining 28 cases were solid with glandular (17 cases) and solid with
tubulopapillary (10 cases). One pure epithelioid case was composed of scattered tumor cells owing to previous treatment effect.

Cytologically, the cells constituting the epithelioid component of the tumors had well-demarcated borders in the majority of the cases (37 cases) with centrally located nuclei and prominent nucleoli. In 3 tumors with a solid pattern, the cells had ample eosinophilic cytoplasm with well-demarcated cell borders, displaying the so-called pavement-like arrangement. Prominent clear cells were observed in 4 tumors. The nuclear grade was 1 to 2 in 5 tumors, 2 in 17, 2 to 3 in 10, and 3 in 17. Four tumors had areas with anaplastic features (nuclear grade 4) characterized by round, polygonal, irregularly shaped, or giant cells with highly pleomorphic nuclei. The mitotic count ranged from none to 29/10 high-power fields (HPFs; 32 cases had <5 mitoses/10 HPFs, 12 had 5-9 mitoses/10 HPFs, and 5 cases had 10 or more mitoses/10 HPFs). Necrosis within the epithelioid component was present in 23 tumors, which was only focal in 4 cases. Mucinous background was present in 11 cases.

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