21 Increased Ki67 labeling index and high nuclear p53 accumulation were observed in high-grade tumors.Klaus J. 18 Some cases reported recently showed neuroendocrine differentiation in the tumor cells staining positive for chromogranin A, synaptophysin, and neuron-specific enolase. 20 Other markers like carbonic anhydrase IX (CAIX), Ulex europaeus agglutinin 1, p63, CK20, GATA3, and smooth muscle actin are negative. CD10, CD15, and RCC marker, which is usually positive in the clear cell variant of RCC, are often negative however, rare cases with positive expression have been reported. The neoplastic cells of both tubules and spindle cells are positive for paired box, transcription factor 2 (PAX2) and PAX8, 18 low-molecular-weight cytokeratin (CK)-that is, CK8/18, CK19 and CK7 ( Figure 6) 19-epithelial membrane antigen, α-methylacyl coenzyme A racemase (AMACR), and E-cadherin 34βE12 and other high-molecular-weight keratins and vimentin show variable expression. Mitoses are usually rare in these tumors, as they are usually low-grade malignancies with a favorable outcome some tumors with sarcomatoid change show increased and atypical mitoses, marked cytologic atypia, and tumor necrosis. These findings were described by Fine et al, 15 who reported a higher occurrence of these findings in the mucin-poor tumors. Other microscopic findings reported in the literature include aggregates of foamy histiocytes, papillations 7 (epithelial tufts that project into the tubular lumina and lack a fibrovascular core), microscopic tumor necrosis, cuffed lymphoplasmacytic infiltrate surrounding tumor cell nests, psammomatous calcifications, and heterotopic bone formation. They found that 10 of the 17 cases were classic MTSCC and the remaining 7 were the mucin-poor variants with little or no extracellular mucin in the stroma. This categorization was based on a percentage of extracellular mucin and the relative percentage of tubules and spindle cells in the tumor after adequate sampling. The study by Fine et al 15 in 2006 expanded the histologic spectrum of MTSCC into 2 variants: classic and mucin poor. 16 The stroma shows extracellular mucin, which may be basophilic or occasionally eosinophilic, with a bubbly appearance. 4, 7 Transitions between the elongated tubules and the spindle cells are commonly seen, and in some tumors, the spindle cell areas can be the principal component, resembling a mesenchymal neoplasm such as leiomyoma or myofibroblastoma. Mucinous tubular and spindle cell carcinoma is a low-grade malignancy, with round nuclei, evenly dispersed chromatin, and occasional nucleoli corresponding 7, 8 to World Health Organization/International Society of Urological Pathology grade 2 however, rare lesions with high-grade atypical nuclei and sarcomatoid change have been described. The tubules may show focally clear cells, oncocytic change, or vacuolations in the cytoplasm. They are often tightly packed and arranged in parallel and sometimes merge into cordlike structures or even form a solid growth pattern. The tubules are round, ovoid, or elongated and anastomosing with a collapsed central lumen. Histologically, the tumor is described by a mixture of tubular and spindle cell components, separated by variable amounts of mucinous stroma 14, 16 ( Figures 3 through 5). In this short review, we highlight the clinical, pathologic, immunohistochemical, and molecular aspects of the tumor, along with the differential diagnoses, clinical behavior, and prognosis. The clinical course and prognosis are not well understood. As the name suggests, MTSCC is morphologically composed of 3 elements: spindle cells, tubules, and extracellular myxoid or mucinous stroma. Since then, fewer than 100 cases 6 have been reported in the literature, with varied clinicopathologic characteristics and molecular features. #SPINDLE CELL CARCINOMA UPDATE#3 Mucinous tubular and spindle cell carcinoma was first included in the 2004 edition of the World Health Organization classification of RCCs, 4 and in the recent update 5 has gained importance owing to prognostic and therapeutic differences. #SPINDLE CELL CARCINOMA SERIES#As a distinct entity, MTSCC was first reported in a series of 4 cases of low-grade renal tumors with myxoid appearance and distal nephron differentiation by Parwani et al. The earliest cases were reported by Ordonez and Mackay 1 and MacLennan et al 2 as “RCC with unusual differentiation, originating in loop of Henle” and “low grade collecting duct carcinoma,” respectively. Mucinous tubular and spindle cell carcinoma (MTSCC) of the kidney is a rare epithelial neoplasm of low malignant potential with characteristic histologic features.
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