SeaGen to Seek FDA Nod After Breast Cancer Drug Hits Goals of Key Study

Xconomy Seattle — 

An experimental breast cancer drug from Seattle Genetics is headed for FDA review after the company reported a pivotal clinical trial met its main goals.

The company has been testing tucatinib as a treatment for advanced or metastatic breast cancer with abnormally high levels of a protein called human epidermal growth factor receptor 2 (HER2), which promotes the aggressive spread of cancer cells.

Seattle Genetics (NASDAQ: SGEN) on Monday announced preliminary study results and said that its targeted therapy, given in combination with two chemotherapies, trastuzumab and capecitabine, met the primary and secondary goals set for the trial. The successful result on the primary goal: The combination of tucatinib with the chemo drugs reduced the risk of the cancer continuing to grow or spread, or the patient dying, by 46 percent compared with results from patients who only received the chemotherapies.

Based on those early results, SeaGen plans to seek FDA approval in the first quarter of 2020 to market the drug as a treatment for HER2-positive breast cancer. The company’s stock price jumped on the news to about $101 at the market close Monday, up 15 percent from Friday’s $87.40 per share closing price.

According to the Bothell, WA-based company, 271,270 new cases of invasive breast cancer are estimated to be diagnosed in the US this year; between 15 and 20 percent of breast cancer cases worldwide have high levels of HER2.

Tucatinib, an pill, targets tyrosine kinase enzymes, which play a key role in cancer growth. Originally developed by another Washington state company, Cascadian Therapeutics, the drug was in late-stage testing last year when SeaGen acquired the company—and its lead drug—for $614 million cash.

SeaGen says that, unlike some other cancer drugs that target those enzymes, tucatinib doesn’t impact another protein, epidermal growth factor receptor (EGFR); inhibiting EGFR can cause serious side effects, including skin rashes and diarrhea.

The most common side effects experienced by the patients in the trial who received tucatinib were diarrhea, hand-foot syndrome, nausea, fatigue, and vomiting; 5.7 percent of those patients stopped participating because of the side effects, compared with 3 percent of patients who weren’t receiving the drug and stopped participating, according to SeaGen.

The company enrolled 612 patients in the study; the data the company disclosed Monday were from the first 480 patients enrolled, as planned. Given the results, the patients in the control group will now be offered the three-drug option. All patients had been previously treated with other cancer drugs: trastuzumab, pertuzumab, and ado-trastuzumab emtansine (T-DM1).

SeaGen was also tracking overall survival in patients who received the trio of drugs; the risk of death was 34 percent lower in that group than for those who didn’t get tucatinib. It also tracked disease progression among a subset of patients whose disease had spread to the brain before the trial started—about half of those enrolled—and found a 52 percent reduction in the risk of disease progression or death. The drug has received an orphan drug designation from the FDA as a treatment for those patients, which gives the company financial incentives to advance its development.

The demonstrated benefit in patients whose cancer had spread to the brain could give the SeaGen drug a competitive advantage, SVB Leerink analyst Andrew Berens wrote in a Monday research note, calling the data in connection to that subset of patients “extremely compelling.”

“The benefit in patients with brain [metastasis] could potentially lead to tucatinib use throughout all lines of therapy in anyone diagnosed with brain [metastasis],” he wrote.

Two other experimental breast cancer drugs that target tumors with abnormally high levels of HER2, Puma Biotechnology’s (NASDAQ: PBYI) neratinib and MacroGenics’ (NASDAQ: MGNX) margetuximab, didn’t show benefit for patients whose disease had spread to the brain, Berens said.

If SeaGen gets the FDA’s OK for tucatinib, the drug will be the second it has taken to market since its founding in 1997. Its first, brentuximab vedotin (Adcetris), a treatment for lymphomas, was approved in 2011.