Primary tumor characteristics and immunohistochemical profile of renal cell carcinoma in serous fluid cytology

Introduction

Renal cell carcinoma (RCC) involves serosal surfaces in 2%-3% of cases, and thus few papers describe serous fluid cytology (SFC) involvement by RCC. This diagnosis is challenging, given its rarity, nondescript cytomorphologic features and infrequent expression of widely used epithelial markers MOC31 and BerEP4. We describe our institutional experience with RCC in SFC specimens.

Materials and methods

Our institutional laboratory information system was queried for SFC specimens from patients with RCC between 2013 and 2023. Cases signed out as “Suspicious for Malignant Cells” and “Positive for Malignant Cells” were included. Patient demographics, immunohistochemical results, primary tumor characteristics, and molecular data were recorded.

Results

Sixty-one cases, 50 pleural, and 11 peritoneal fluid specimens were identified. Fifty (50) were signed out as positive for malignancy and 11 were signed out as suspicious for malignancy. MOC31 and BerEP4 were positive in 59% and 55% of cases, respectively. PAX-8, CA9, CD10, and RCC were positive in 85%, 82%, 73%, and 29% of cases, respectively. Primary tumor histologic subtypes included 39 clear cell, 6 papillary, 1 chromophobe, and 15 were not further subclassified. Fifty-nine percent (59%) of cases had a nuclear grade of 4%, and 37% had sarcomatoid or rhabdoid differentiation. Seventy-one percent (71%) of cases had stage 3 or 4 disease.

Conclusions

RCC metastases to serosal surfaces are more likely to be seen in patients with higher disease stage, high nuclear grade, and sarcomatoid or rhabdoid differentiation. MOC31 and BerEP4 performed poorly in this setting. We recommend the addition of cytokeratins, PAX-8, CD10, and CA-9 to confirm metastatic involvement.