Proteomic profiling identifies novel diagnostic biomarkers and molecular subtypes for mucinous tubular and spindle cell carcinoma of the kidney

Mucinous tubular and spindle cell carcinoma (MTSCC) is a relatively rare renal epithelial neoplasm resembling type 1 papillary renal cell carcinoma (PRCC) morphologically and immunohistochemically. The accurate diagnosis of MTSCC remains a challenge. Here, by using proteomic profiling, we characterized MTSCC and PRCC to identify diagnostic biomarkers. We found that the MTSCC tumor proteome was significantly enriched in B‐cell‐mediated immunity when compared with the proteome of adjacent normal tissues of MTSCC or tumors of PRCC. Importantly, we identified MZB1, VCAN, and SOSTDC1 as diagnostic biomarkers to distinguish MTSCC from the solid variant of type 1 PRCC, with an AUC of 0.985 when combined. MZB1 was inversely correlated with tumor clinical stage and may play an anti‐tumor role by activating the complement system. Finally, unsupervised clustering revealed two molecular subtypes of MTSCC, displaying different morphology, expression signatures of oxidative phosphorylation, and aggravation. In summary, our analyses identified a three‐protein diagnostic panel and molecular subtypes for MTSCC. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.