26. Chromosomal characterization of six new cases of Mucinous tubular and spindle cell carcinoma of the kidney

      Mucinous tubular and spindle cell carcinoma (MTSCC) is a rare subtype of renal cell carcinoma (RCC), recognized as a distinct entity in the 2004 World Health Organization (WHO) tumor classification. It has indolent clinical behavior and characteristic histological features with an admixture of low-grade elongated tubules and bland spindle cells in a mucinous or myxoid stroma. Genetic studies of MTSCC are limited with only 5 reported cases of karyotype analysis, less than 80 cases for chromosome copy number analysis and 15 with next generation sequencing studies. Recurrent and distinct genetic abnormalities including losses of chromosomes 1, 4, 6, 8, 9, 13, 14, 15, and 22, while lacking gains of chromosomes 7 and 17 and loss of Y chromosome, have been shown to serve as an important supporting evidence for the differential diagnosis of MTSCC. Due to the female predominance feature of MTSCC, genetics studies in male patients are extremely underpowered. Here, we present G-band karyotype analysis of 6 MTSCC tumors (3 males and 3 females), ages range from 32-88 years. In 5 grade 1 tumors we identified chromosomal abnormalities, i.e. -1,-4,-6,-8,-9,-13,-14,-15, -22, that have been previously described in the literature. The 6th case, a high grade MTSCC with lymphatic invasion showed a distinct hyperdiploid karyotype 52,X,-Y,+3,+7,+16 × 2,+17,+20,+21. We assume this is due to whole genome duplication of hypodiploid karyotype with further loss of chromosomes during disease progression. Interestingly, we identified a consistent loss of chromosome X in all three female cases and loss of Y in all three male cases. Further details will be presented. This is the largest series of MTSCC karyotype analysis published so far. The present study highlights the importance of chromosomal analysis in differential diagnosis of MTSCC. Expanded next generation sequencing studies may provide further clues in understanding the molecular basis of MTSCC.
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