Sarcomatoid change has been well documented in the various subtypes of renal cell carcinoma (RCC) and its presence is known to portend a worse prognosis in RCC. Mucinous tubular and spindle cell carcinoma is a RCC subtype, which is defined as polymorphous histology wherein the spindled epithelial cell is an inherent carcinomatous component. Many of these putatively low-grade tumors have been previously misdiagnosed as unclassified or sarcomatoid papillary RCC. We present 2 examples of hitherto undescribed sarcomatoid change in mucinous tubular and spindle cell carcinoma in a 71-year-old woman and an 80-year-old man who both underwent a radical nephrectomy procedure. In addition to the classic mucinous tubular and spindle cell carcinoma morphology, both cases had a sarcomatoid component characterized by predominantly high-grade spindle cells, solid pleomorphic epithelioid cells, and malignant fibrous histiocytoma-like storiform patterns. Sarcomatoid change comprised 60% and 20% of the tumors, respectively. Unlike the spindle sarcomatoid cells, the inherent spindle cell elements of mucinous tubular and spindle cell carcinoma had distinctively low-grade cytology and occasionally blended with tubular structures and variable mucinous stroma. The sarcomatoid cells were associated with significant necrosis, marked nuclear pleomorphism, mitoses of up to 5/10 high power field, higher proliferation fraction (MIB1), and loss of alpha-methylacyl-CoA racemase or cytokeratin 7 expression. Cytogenetic analysis in 1 tumor showed loss of chromosomes 14 and 15 and gains of chromosomes 2, 5, 7, 9, 10, 12, 17, 19, 20, 22, and X. Widespread metastasis to lymph nodes, bones and lungs occurred in one patient who succumbed 9 months after nephrectomy. Helpful features in distinguishing spindle cells of sarcomatoid component versus that of the native tumor include the presence of high-grade cytology, expansile growth with loss of typical imperceptible blending with the tubulo-papillary component, extensive necrosis, high mitotic activity, high proliferation fraction, and loss of expression of alpha-methylacyl-CoA racemase that contrasted the classic areas. Distinction of the sarcomatoid histology from inherent spindle cell component of mucinous tubular and spindle cell carcinoma is important because of its unfavorable prognostic implication.
