MIB-1 (Ki-67) immunostain demonstrated a higher proliferation index in sarcomatoid regions (Fig. 2F). Both chromophobe and spindle cell components were evaluated by electron microscopy. Ultrastructural features typical of CRCC, such as cytoplasmic vesicles and abundant mitochondria with disrupted, tubulovesicular, or absent cristae were seen in the chromophobe component, in addition to multiple contiguous intercellular attachments consistent with epithelial differentiation. The spindle cell component exhibited ultrastructural

features consistent with 2 distinct cell populations, one being myofibroblastic with subplasmalemal filaments and abundant rough endoplasmic reticulum and the other being check details consistent with a chromophobe cell phenotype, as shown by the presence of abundant abnormal mitochondria. Normal, epithelial, and sarcomatoid components of tumor were microdissected and deoxyribonucleic acid Ponatinib purchase extracted for loss of heterozygosity (LOH) analysis using polymorphic markers for chromosomes 3p25, 1p35-36, and 1q42-43. There was LOH in chromosomes 1p and 1q in tumor cells of typical chromophobe morphology. In contrast, tumor cells of spindle cell morphology displayed LOH in chromosomes 3p (Fig. 3) in addition to 1p and 1q. Chromophobe subtype of RCC is uncommon, and

its sarcomatoid dedifferentiation is rare. Few cases of sarcomatoid CRCC have been reported.4 and 5 The mean age of presentation of sarcomatoid CRCC is higher than sarcomatoid clear cell RCC, suggesting that sarcomatoid change occurs in long-standing CRCCs, such as in our current case. Sarcomatoid CYTH4 component represents poorly

differentiated transformation that occurs in any histologic subtype.6 and 7 Clinicopathologic studies confirm that sarcomatoid transformation is associated with dismal prognosis. It is important to emphasize that most studies refer to sarcomatoid differentiation in the most common subtype of RCC, that is, clear cell type, and there is limited information about sarcomatoid change in the chromophobe subtype. Metastasis of CRCC is deemed rare. Contrary to the belief that it is usually the sarcomatoid component that metastasizes to lymph nodes,5 and 8 we find lymph node metastasis of both chromophobe and spindle cell components. An unexpected finding in the current case is the unusual pattern of lymphangitic spread. Multiple foci of the sarcomatoid tumor were in lymphatic vessels and permeating retroperitoneal and perirenal adipose tissue. We considered lymphangiosarcoma in our differential diagnosis. However, morphologic comparison with the primary renal tumor and immunophenotype (cytokeratin AE1/AE3 positivity) was in favor of lymphangitic carcinomatosis by sarcomatoid CRCC. There are only few instances of lymphangitic carcinomatosis of clear cell RCC.