MTSCC has a gross appearance close to papillary RCC. Microscopically, it has three histologic components: mucin, tumor cells forming tubules, and<unk>  cells. It is characterized by the proliferation of cuboidal and<unk>  cells arranged in<unk>  or sheet-like arrays, typically with a<unk>  or myxoid background. Immunohistochemical staining IHC close to papillary RCC profile: CK7+, AMCAR+, CD10-. Morphological variants MTSCC can be a difficult diagnosis due to its morphologic heterogeneity. Several morphological variants have been described, as the ‘‘mucin-poor variants’’, showing a predominance of<unk>  or<unk>  cell components and only minimal pale<unk>  background. Focal papillations or papillary cores and foamy histiocytes can also be seen, creating confusion with type 1 papillary RCC. Helpful features for diagnosis are bland cytologic features and adjacent<unk>  and<unk>  cell components. Focal areas of clear cells and oncocytic cells can also be present. Differential diagnosis Papillary renal cell carcinoma: MTSCC may have some morphologic similarities to the more common papillary renal cell carcinoma (papillary RCC), particularly the basophilic tumors (type 1 papillary RCC) with prominent solid growth pattern with sarcomatoid transformation.
Mucinous tubular and spindle cell carcinoma
Epithelial-myoepithelial carcinoma
Papillary adenocarcinoma
Clear-cell adenocarcinoma
Lymphoepithelioma-like carcinoma
Adenomatoid tumor
Hyalinizing clear cell carcinoma
Papillary tumor