A rare case of FH-deficient renal cell carcinoma with signet ring cells features.

Fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) is a clinically aggressive tumor with high rates of progression and mortality. A wide range of morphological variations has been observed in FH-deficient RCC, initially described as type 2 papillary RCC or unclassified RCC. Here, we report a case of FH-deficient RCC with rare signet ring cells features. The patient was diagnosed with FH-deficient renal cell carcinoma and suspected to have hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome. After 4 months, pulmonary metastasis occurred in the patient. We herein describe the first case of FH-deficient renal tumor with signet ring cells features, which expands the morphological spectrum of this tumor. More importantly, this variant can be a diagnostic pitfall, we emphasize that pathologists should consider not only the diagnosis of metastatic signet ring cell carcinoma and ALK rearrangement renal cell carcinoma but also FH-deficient renal cell carcinoma.