By Vishwadha Chander and Saumya Joseph

(Reuters) – The U.S. Food and Drug Administration approved Blueprint Medicines Corp’s oral therapy to treat a rare form of cancer that affects the stomach and small intestine, the agency said on Thursday.

The FDA’s decision makes the therapy, Ayvakit, the first treatment for a small subset of patients with a mutation of the cancer called gastrointestinal stromal tumor (GIST).

Blueprint said it expects to make Ayvakit available through a limited specialty pharmacy network in the United States within a week, with a wholesale acquisition cost or list price of $32,000 for a 30-day supply, regardless of dosage.

The list price is not necessarily what patients actually pay as “out-of-pocket” costs vary based on the duration of the treatment and individual healthcare plans.

GIST tumors, which usually begin in the stomach or small intestine, are a type of soft-tissue sarcoma. Patients are at risk of the cancer recurring even after successful surgery to remove tumors.

About 5,000 Americans are diagnosed with the cancer every year. With Ayvakit, Blueprint is looking to target about 6% of these patients whose cancers are driven by PDGFRA exon 18 mutations.

In patients with the mutation, the cancer tends to progress in a median of about three to four months after being treated with currently available therapies.

Ayvakit works by selectively inhibiting the drivers of the mutation and was found to be well tolerated and effective in more than 80% of patients it was tested in, the company said.

“We’re not only having significant impact on shrinking their tumors, we’re also keeping them disease progression free for very long periods of time,” Chief Operating Officer Kate Haviland told Reuters in a phone interview.

Balancing off-target effects has helped patients stay on the treatment, said Haviland, adding that the company has seen patients continue the therapy for nearly four years.

GIST patients who have undergone surgery are typically given Novartis AG’s Gleevec. However, the drug has not been effective in treating patients with the mutation targeted by Blueprint.

“It’s a big improvement for patients and a very big milestone for the company… but in terms of sales, this exact indication is not huge,” said Cowen and Co analyst Marc Frahm who expects Ayvakit peak sales of $68 million by 2032.

Blueprint is also pursuing FDA approval for Ayvakit in patients with GIST who have exhausted all other options of care – a much larger population of patients.

(Reporting by Vishwadha Chander and Saumya Sibi Joseph in Bengaluru; Editing by Aditya Soni)