Metastatic Papillary Renal Cell Carcinoma: Treating Without a Real Evidence Base
Nearly every major RCC trial was built around clear cell histology — the actual decision for his papillary tumor rests on a single dedicated trial and a body of extrapolated evidence nobody is fully confident applies to him.
G.N., a 61-year-old man, has spent his career as a long-haul truck driver, logging routes across half the country and describing the highway, only half-joking, as the place he's spent more time than his own living room. A left nephrectomy for what was read at the time as clear cell renal cell carcinoma was five years ago; central pathology review after he developed pulmonary and hepatic metastases reclassified the original tumor as type 2 papillary renal cell carcinoma, a distinct histologic and molecular entity that most of the major RCC trials — CheckMate 214, KEYNOTE-426, CLEAR, CheckMate 9ER — either excluded outright or enrolled in numbers too small to draw any real conclusion from. His disease is now metastatic, and the team is choosing his first-line systemic therapy from an evidence base built almost entirely for a different tumor type.
The one dedicated randomized trial in this disease, SWOG 1500, opened with four arms — cabozantinib, sunitinib, everolimus, and crizotinib — but closed the everolimus and crizotinib arms early for futility, so its result is a comparison of cabozantinib against sunitinib, in which cabozantinib produced a superior response rate and progression-free survival without a significant overall survival difference. Real, disease-specific evidence, from a smaller trial than clear-cell RCC's own base and with no checkpoint-inhibitor-containing arm ever tested against it. The alternative is extrapolating one of clear cell RCC's immunotherapy combinations onto his papillary tumor, on the reasoning that PD-1 blockade's mechanism isn't obviously histology-specific — a plausible argument, but one resting on mechanism rather than any trial actually testing it in this disease. His MET status has not yet been tested, a gap that matters directly given cabozantinib's specific MET-inhibiting activity and papillary RCC's known, if variable, rate of MET pathway alterations. The original clear-cell reading stood unquestioned for five years, through his nephrectomy and every scan afterward, until the new metastatic tissue prompted the pathologist to send the case for central review — a reclassification he described at his last visit as feeling less like a new diagnosis and more like being told the last five years of his own chart had been about someone else's tumor.
Choosing first-line therapy without a clear standard
I'd start cabozantinib. SWOG 1500 is the one dedicated randomized trial we actually have in papillary RCC. It dropped the everolimus and crizotinib arms early for futility, and against sunitinib — the arm that finished — cabozantinib was superior on response rate and progression-free survival. That's real, disease-specific evidence, even if it's a smaller trial than what clear cell RCC has.
I'd want to at least consider a checkpoint-inhibitor combination extrapolated from clear cell RCC. PD-1 blockade's mechanism isn't obviously restricted to one histology, and the depth of response we see with the immunotherapy combinations in clear cell disease is substantial. I don't think a smaller single-agent trial should be treated as automatically settling this just because it happens to be disease-specific.
Disease-specific isn't automatically better evidence if the trial is small enough that a checkpoint-inhibitor arm was never even tested against it.
Before either regimen starts, I'd want his MET status back. Cabozantinib's activity in papillary RCC wasn't uniform across subtypes in SWOG 1500, and MET alterations are specifically relevant to why it works when it works. That result could make this a much easier call one way or the other, rather than choosing between two evidence bases in the abstract.
Agreed: cabozantinib started now given SWOG 1500's disease-specific evidence, with MET testing sent concurrently rather than delaying treatment for the result.
Not agreed, and left open pending the MET result:
All three physicians would treat cabozantinib as the clearly preferred choice, with mechanism and trial evidence aligned.
The second oncologist would revisit whether an immunotherapy-based combination should be considered at the first sign of inadequate response, rather than continuing cabozantinib by default.