Do clear cell papillary renal cell carcinomas have malignant potential?

There have been no recurrences or metastases of clear cell papillary renal cell carcinoma (CCPRCC) in 268 reported cases with follow-up in the English-language literature. We identified all our cases of CCPRCC (1990 to 2013), reviewing all cases that preceded the formal designation of the entity. Immunohistochemical stains were performed on 32 cases during their initial workup. In addition, stains for carbonic anhydrase IX and cytokeratin 7 were performed on 2 cases, one with atypical follow-up and the other with a more compact morphology, although not performed initially. An extended panel with AMACR, CD10, and renal cell carcinoma (RCC) was added to the case with atypical follow-up. Fluorescence in situ hybridization for chromosomes 3p, 7, and 17 was performed on the latter case and on another clinically presumed metastatic tumor. In classic cases, immunohistochemical staining was not performed. Fifty-eight patients (31 women; 27 men) with follow-up data were included in our study; 39 cases were from our consult service. The patients' ages ranged from 36 to 83 years. Thirty-five patients had cystic or partially cystic lesions; 6 tumors were multifocal, 3 of which were bilateral. The majority (53 patients; 91.4%) presented with stage pT1 disease (size range, 0.2 to 8 cm), 2 patients presented with pT2 disease (8.5 and 10.3 cm), 1 patient presented with pT3 disease (6.5 cm sarcomatoid RCC focally extending out of the kidney), and pathologic stage was unavailable in 2 cases. Treatment consisted of 29 partial nephrectomies, 26 radical nephrectomies, 2 cryoablations, and 1 cyst ablation. The resection margins were negative in all but one case, with this case disease free after a 26-month period. Two patients had intraoperative tumor disruption and were disease free at 9 and 34 months. Five patients had synchronous ipsilateral renal cell carcinomas (non-CCPRCC). Mean follow-up time was 21 months (range, 1 to 175 mo), with all but 3 patients having no evidence of disease. One patient was presumed to have contralateral disease on the basis of imaging findings and is alive and well 37 months after multiple partial nephrectomies. Metastatic disease to the lung was clinically presumed in 1 patient in whom a higher-grade lesion may have been missed during sampling of the predominantly cystic pT1b tumor and tissue confirmation of the metastases was not obtained. Another case presented with multiple skeletal and pulmonary metastases 8 months after resection of pT3 sarcomatoid CCPRCC. The patient with the sarcomatoid RCC died of multifocal skeletal and pulmonary metastatic disease 13 months after resection of the renal tumor. Our study, the largest to date with follow-up, along with others, suggests that pure CCPRCC is an indolent tumor and should be renamed "clear cell papillary neoplasm of low malignant potential" to reflect their biology.