Clear cell papillary renal cell carcinoma (CCPRCC), a recently identified, rare type of renal tumor, appears to have an indolent course with low risk of either local invasion or distant metastasis, results of a small retrospective study suggest.

Among 25 patients with CCPRCC followed for as long as 119 months, there were no cases of local recurrence or distant metastasis, reported Wei-Jen Chen, MD, of Tapei (Taiwan) Veterans General Hospital, and colleagues.

“Based on our findings, CCPRCC has an indolent behavior even if the patients are immunosuppressed or if they receive less invasive therapy. Microscopically, CCPRCC is considered to be a tumor of low malignant potential, as all tumors in our series were of low nuclear grade,” they wrote in a study published online in the Journal of the Chinese Medical Association.

“Whenever the diagnosis is made in a high grade renal tumor, it should be carefully re-confirmed by either cytogenetic or molecular genetic methods,” the authors reported.

CCPRCC was newly recognized as a distinct renal malignancy in the 2016 World Health Organization Classification of Tumors of the Urinary System and Male Genital Organs. The classification describes CCPRCC as “a renal epithelial neoplasm composed of low-grade clear epithelial cells arranged in tubules and papillae with a predominantly linear nuclear alignment away from the basement membrane.”

Although rare, these tumors account for up to 5% of all resected renal tumors, and arise sporadically in patients with end-stage renal disease (ESRD) and von Hippel-Lindau syndrome, the classification states, adding that “according to current knowledge, these tumors have indolent behavior.”

To see if they could verify that last statement, Dr. Chen and associates collected data on all patients diagnosed at their institution with CCPRCC from January 2008 through September 2016.

They identified a total of 25 patients (11 men and 14 women) with a mean age at diagnosis of 62.8 years. Of this group, three patients with poor general condition underwent cryotherapy after a biopsy-confirmed diagnosis of CCPRCC.

All of the remaining 22 patients underwent surgical resection. Of this group, four had ESRD; three of these patients had received a kidney transplant prior to diagnosis of CCPRCC in the native kidneys, and one had three tumors over both kidneys.

“Three patients had other types of synchronous RCC; one with acquired cystic kidney disease-associated RCC, and the others with ccRCC. All CCPRCCs were localized and low grade (pT1a- pT1b, Fuhrman grade 2), and all of the patients are currently alive with no evidence of disease,” the investigators wrote.

Mean follow-up was 49.7 months (range 12 to 119 months).

One additional patient who was not included in the series was initially diagnosed with CCPRCC with lung metastasis. This patient, who died 3 years and 8 months after cytoreductive nephrectomy, had a clinical course distinct from that of all the other patients, leading the investigators to reexamine his kidney specimen with whole-exome sequencing. The sequencing led to a revision of the diagnosis to clear cell RCC.

The investigators noted that clear cell RCC, papillary RCC, and translocation RCC are three RCC subtypes that should be considered in the differential diagnosis of CCPRCC.

The investigators did not report a study funding source. They reported having no conflicts of interest relevant to the subject matter or materials discussed in the article.

SOURCE: Chen W-J et al. J Chinese Med Assoc. 2018 July 20. doi: 10.1016/j.jcma.2018.04.005.

Rare clear cell papillary RCC has indolent course