Biphasic Papillary Renal Cell Carcinoma Is a Rare Morphologic Variant with Frequent Multifocality: A Study of 28 Cases

Abstract

Aims

To further characterize biphasic squamoid renal cell carcinoma (RCC), a recently proposed variant of papillary RCC.

Methods and results

We identified 28 tumors from multiple institutions. They typically demonstrated two cell populations - larger cells with eosinophilic cytoplasm and higher-grade nuclei, surrounded by smaller, amphophilic cells with scanty cytoplasm. The dual morphology was variable (median 72.5% of tumor, range 5-100%); emperipolesis was found in all cases. Male-to-female ratio was 2:1, median age 55 years (range 39-86). Median tumor size was 2 cm (range 0.9-6.5). Pathologic stage pT1a was found in 21 cases, pT1b in 3, pT3a and pT3b in 1 patient each (2 not available). Multifocality was found in 32%: multifocal biphasic RCC in 1, biphasic + papillary RCC in 2, biphasic + clear cell RCC in 3, biphasic + low-grade urothelial carcinoma of renal pelvis in 1, and biphasic + Birt-Hogg-Dubé syndrome in 1 case. Positive immunostains included: PAX8, CK7, AMACR, EMA, and vimentin. Cyclin D1 was expressed only in the larger cells. Ki67 index was higher in the larger cells (median 5% vs. ≤1%). Negative stains included: CA9, CD117, GATA3, WT1, CK5/6 and CK20; CD10 and 34βE12 were variably expressed. Gains of chromosomes 7 and 17 were found in 2 evaluated cases. Follow-up was available for 23 patients (median 24 months, range 1-244): 19 were alive without disease, 1 was alive with recurrence, 1 died of disease (2 died of other causes).

Conclusions

Biphasic papillary RCC is a rare variant of papillary RCC, which is often multifocal.

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