Seattle Genetics chalks up further clinical trial success in solid tumors

Seattle Genetics could move beyond its core focus in blood cancers and into the solid tumor setting, if positive early-stage data is backed up by further trials.

The company said its antibody-drug conjugate SGN-LIV1A has shown efficacy in patients with triple-negative metastatic breast cancer—a particularly hard-to-treat patient population—in a Phase I trial presented at the San Antonio Breast Cancer Symposium (SABCS).

The drug consists of a LIV-1-targeted monoclonal antibody linked to the cell-killing payload monomethyl auristatin E, and is one of four candidates Seattle Genetics has in clinical trials for solid tumors.

Analyst at Leerink said the results, which showed a 37% overall response rate in patients not responding anymore to approved therapies, were "impressive" for a single agent and give an indication that solid tumors could be "a source of upside for the stock."

Approximately 15% to 20% of the 1.67 million new cases of breast cancer each year are triple negative, which means they lack expression of three biomarkers (i.e. estrogen receptors, progesterone receptors, and HER2) that make them candidates for targeted therapies. They tend to be more aggressive and patients generally have a poorer prognosis.

It has been 5 years since Seattle Genetics' Adcetris (brentuximab vedotin) reached the market as a second-line therapy for classical Hodgkin lymphoma (HL), and since then more than 30,000 lymphoma patients have been treated with the drug. 

Near term, investor focus will likely continue to be on label expansion opportunities for Adcetris, which the company expects to post North American sales of $260 to $270 million this year.

Seattle Genetics recently reported positive results from a pivotal trial in CD30-expressing cutaneous T-cell lymphoma (CTCL) which may support filing for a follow-up indication. A trial that could support first-line use in HL is due to generate results next year. Meanwhile, its vadastuximab talirine (SGN-CD33A) drug candidate for acute myeloid leukemia (AML) started a registration trial in May that is scheduled to provide data in 2019.

"While much investor focus has been on label expansion opportunities for Adcetris in Hodgkin lymphoma and the emerging profile of SGN-CD33A in AML, in our view solid tumors represent a key area of potential growth," said Leerink in a research note.

They suggest the data on SGN-LIV1A look encouraging compared to other investigational agents in development for triple-negative breast cancer, including other antibody-drug conjugates from Immunomedics (sacituzumab) and Celldex (glembatumunab) as well as checkpoint inhibitors such as Merck & Co.'s Keytruda (pembrolizumab).