Dr. Tawee Tanvetyanon at the Moffitt Cancer Center in Tampa rarely sounds this enthused about the future prospects for patients with pleural mesothelioma.
Finally, he has something promising to offer.
“This is exciting. We now can offer something with realistic hope,” he told Asbestos.com. “We haven’t had anything like this for mesothelioma in a long time. I really look forward to speaking with these patients now.”
Moffitt recently became the first multidisciplinary specialty center to begin enrolling mesothelioma patients in a trial that will evaluate the efficacy of combining CRS-207 with pembrolizumab — two immunotherapy drugs that already showed effectiveness individually — in a second-line setting.
“Of course, the hope is that we see significant tumor shrinkage. We already know, we have data, that each of these agents will work in a number of patients,” Tanvetyanon said. “There is good reason to think that combining the two will work even better, a one-plus-one-equals-three synergy.”
Two competing pharmaceutical companies have worked together to make this latest, anti-cancer combination a reality for mesothelioma patients.
Aduro Biotech, based in Berkeley, California, produces CRS-207, which uses the genetically engineered Listeria virus to trigger an immune response to a specific tumor antigen.
Merck, a multinational company, developed pembrolizumab (Keytruda), a well-known immunotherapy agent that targets a particular cellular pathway. Keytruda already has received FDA-approval for melanoma, head and neck cancers and certain non-small cell lung cancers.
An estimated 30 percent of patients receiving CRS-207 alone experienced mesothelioma tumor shrinkage in one recent study. A combination of CRS-207 with chemotherapy, in another trial, resulted in a 59 percent partial response and a 35 percent stable disease rate.
Almost half of mesothelioma patients in one recent study experienced initial tumor reduction with Keytruda. The average time before disease progression was six months.
“One exciting thing about immunotherapy, across all cancer sites, is a tendency to produce long-lasting effects,” Tanvetyanon said. “If it works, it tends to work for a long time.”
Other clinical trial sites that started or will soon begin recruiting patients:
The trial regimen will be administered in three-week cycles. Keytruda, in the first cycle, will be given intravenously on day 1, and CRS-207 will be given intravenously on day 2. If both are well tolerated, they will be given on the same day in subsequent cycles.
After four cycles, only Keytruda will be given every three weeks, while CRS-207 will come every six weeks.
Cycles will continue for up to 24 months if investigators continue to see the clinical benefit. The trial began in June and is expected to run through 2019.
To qualify for this treatment study, patients must already have received one or two prior anti-cancer therapies, at least one of which was chemotherapy.
Pleural mesothelioma, which is caused by long-ago exposure to asbestos, typically comes with a grim prognosis. The majority of patients live less than 18 months after diagnosis.
For some, this trial is expected to extend lives significantly.
“Clinical trials like this are the way to go,” Tanvetyanon said. “Generally, the treatment in a trial has to be at least as good as or better than standard of care. In a clinical trial, the way they are set up, a patient is monitored more closely and gets more attention. And the drugs are free. I’d highly recommend it, if you qualify.”
There currently is no FDA-approved second-line treatment. Less than 25 percent of patients even qualify for aggressive surgery. After chemotherapy stops working, which it normally does, patients are left with no real choices.
“It may take a few more years before you see this [immunotherapy combination] become mainstream treatment,” Tanvetyanon said. “But we’ve already seen lots of studies that suggest this might work well. I’m excited to see where it goes.”