Drug Development

Little Stemline grabs a big ‘breakthrough’ title for its pivotal-stage cancer drug

Back at the big ASCO meeting in Chicago last June, little New York-based Stemline Therapeutics $STML was largely left on the sidelines by a few big acts in oncology R&D that hogged the spotlight. But its snapshot of highly promising Phase II data for a lead drug didn’t escape the attention of the FDA, which has now blessed its work with a breakthrough drug designation.

Naveen Pemmaraju, MD

Naveen Pemmaraju, MD Anderson Cancer Center

The BTD was provided for SL-401, and the news triggered a 20% spike in the company’s share price. Stemline got its IPO out at the beginning of the biotech boom in 2013 and prospered on Nasdaq. But like a lot of biotechs, the company is now trading for far less than half of its two-year high after investors recalibrated their thinking about risk and potential rewards in the last six months.

MD Anderson’s Naveen Pemmaraju journeyed to Chicago to review the first round of promising results for a pivotal mid-stage study for SL-401 on blastic plasmacytoid dendritic cell neoplasm (BPDCN), a rare and deadly hematologic malignancy. He highlighted:

An 89% (17/19) overall response rate (ORR) in BPDCN, with a 100% (12/12) ORR in first-line patients and a 71% (5/7) ORR in relapsed/refractory patients, including one compassionate use patient (see Table 1). In 12 evaluable first-line patients (all doses), there were 9 complete responses (CR) and 2 clinical complete responses (CRc). CRc is defined as a CR in non-skin affected organs with marked gross clearance of skin lesions and residual microscopic skin disease. In the 10 evaluable first-line patients treated at 12 ug/kg/day, the CR/CRc rate was 100% (8 CR and 2 CRc). In the 7 evaluable relapsed/refractory BPDCN patients, including one treated on a compassionate use basis, the ORR rate was 71%, which included 1 CR and 1 CRc (29% CR/CRc rate) and 3 partial responses (PR).

Pemmaraju also highlighted signs of a possible durable response. “75% (9/12) first-line BPDCN patients treated at 12 ug/kg/day remained relapse-free (1+-13+ months),” the company reported. And more work is being done on acute myeloid leukemia and myeloproliferative neoplasms.

The BTD has become a common feature on the R&D landscape. Intended to speed the clinical journey of new drugs with the potential to alter the landscape of medical treatment, it’s become a title that is now often handed out to the same drug for multiple indications. Big Pharmas love to boast about their string of BTDs. Stemline, though, is a somewhat more unusual case; a small biotech with a $141 million market cap that can now boast of an open door at an FDA that has proved particularly willing to accelerate approvals for new oncology drugs.

That’s something that investors liked to see, at least briefly.

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