Rare Diseases Report 2021

Rare GU cancers: Overcoming obstacles through collaboration, novel trial design


 

Cabozantinib and nivolumab with or without ipilimumab

Dr. Apolo is leading a similar basket trial (NCT02496208) that is testing cabozantinib plus nivolumab with or without ipilimumab.

“What we’re doing is using immunotherapy and a targeted therapy that work in standard urothelial carcinoma and renal cell carcinoma,” Dr. Apolo said. “But really, we don’t know the activity in these rare GU tumors. … There’s still so much we don’t understand about what the driving mutations are, and how we can best target them.”

Most recent data, published in Journal of Clinical Oncology, include 122 patients with metastatic GU tumors, including urothelial carcinoma, clear cell renal cell carcinoma, bladder adenocarcinoma, and other rare GU cancers.2

Among these patients, 54 were in the phase I dose-finding cohort (eight escalating doses) and 64 were in the dose-expansion cohorts.

After a median follow-up of 40.4 months, 64 patients received the dual combination, whereas 56 received the triplet regimen. The ORR for 108 evaluable patients was 38%, including 12 complete responses (11.1%) and 29 partial responses (26.9%). The largest disease cohort, for urothelial carcinoma, included 33 patients and was associated with an ORR of 42.4%, with a complete response rate of 21.2%. Objective response rate was highest for squamous bladder cancer (85.7%; n = 7), followed by clear cell renal carcinoma (62.5%; n = 16), renal medullary cancer (50%; n = 2), penile cancer (44.4%; n = 9), small cell bladder cancer (33.1%; n = 3), bladder adenocarcinoma (20%; n = 15), and prostate cancer (11.1%; n = 9). No responses were seen in six patients with germ cell tumors.

Adding ipilimumab appeared to have a minimal impact on toxicity. Grade 3 or 4 treatment-related adverse events (AEs) occurred in 84% of patients in the dual combination group, compared with 80% receiving the triplet regimen. Most common AEs were hypophosphatemia (16-25%), lipase elevation (20%), fatigue (18-20%), ALT elevation (5-14%), AST elevation (9-11%), diarrhea (9-11%), and thromboembolic event (4-11%). One patient taking the triplet regimen had grade 5 pneumonitis.

These positive phase I results have paved the way for the phase II ICONIC trial (NCT03866382), a national study available through the Alliance Cooperative Group. The trial is currently recruiting, with an estimated enrollment of 224 patients with rare GU tumors.

The ICONIC trial is just one of several studies that Dr. Apolo is conducting for patients with rare GU cancer. “I have several bladder cancer trials where I’m accepting rare GU tumors to enroll,” she said, noting that efficacy signals in these exploratory cohorts may be pursued with expansion studies like ICONIC.

This inclusive strategy is uncovering promising new treatments for some rare GU malignancies, but the rarest of the rare tumor types remain challenging to study, Dr. Apolo said, because very small sample sizes can preclude significant data. “Although we do have the referral base at the NCI, we still get a small number of a lot of rare tumors,” Dr. Apolo said. “What I end up having, a lot of time, are small subsets of rare tumors – I’ll have 4 of one kind, 10 of another.” This situation means that sometimes, time and resources must be focused where they are needed most.

“Sometimes I actually have to decide which are the more common rare tumors so I can study them in a larger cohort,” Dr. Apolo said. “It can have more clinical impact within the community of that rare tumor.” Dr. Apolo described the inherent conflict involved in this decision, but also, its ultimate necessity.

“It’s what you don’t want to do, but you end up doing,” she said. “Because you want to be inclusive and include the rare, rare tumor, but sometimes you just can’t get enough numbers to see if there’s actually a difference [in efficacy]. If it doesn’t work in one patient, does that mean it doesn’t work at all? You need more numbers to really test the efficacy of therapy.”

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