Updated with new information.
SAN FRANCISCO (TheStreet) -- The use of Seattle Genetics' (SGEN) Adcetris as a maintenance therapy after a stem-cell transplant in "high risk" Hodgkin lymphoma patients led to a 20 percentage point improvement in relapse rates compared to a placebo after two years of follow-up, researchers reported Saturday.
The new Adcetris data comes from a phase III study known as AETHERA, which is being presented in full at the American Society of Hematology annual meeting underway here. Next year, Seattle Genetics intends to seek approval from regulators to expand the use of Adcetris into a larger pool of Hodgkin lymphoma patients based on the AETHERA study results.
The AETHERA study enrolled 327 Hodgkin lymphoma patients who had undergone stem-cell transplant to put their disease into remission but who still had certain characteristics which made them more likely to relapse. Between 30 and 45 days after transplant, the patients were randomized to receive treatment with Adcetris or a placebo for one year.
After two years of followup, 65% of Adcetris patients had no evidence of disease progression compared to 45% of patients treated with a placebo, according to new details from the AETHERA study disclosed Saturday at an ASH-sponsored media briefing.
"This is the first study in lymphoma to demonstrate that the addition of a maintenance drug after transplant can markedly improve patient outcomes," said Dr. Craig Moskowitz of Memorial Sloan Kettering Cancer Center in New York. Moskowitz was the lead investigator in the AETHERA study.
In September, Seattle Genetics first announced the AETHERA study achieved its primary endpoint, showing maintenance therapy with Adcetris led to a 43% reduction in the risk of disease progression compared to placebo.
Despite delaying disease progression, treatment with Adcetris did not prolong survival compared to placebo in the phase III study at this analysis, which the company blames partly on placebo patients "crossing over" to receive Adcetris once their disease progressed. Another survival analysis of the study will be conducted in 2016. Adcetris' safety profile was "generally consistent" with previous studies, the company said.
Adcetris is already approved to treat more advanced Hodgkin patients who don't respond to a stem cell transplant or who are not eligible for stem cell transplants. Seattle Genetics estimates there are about 1,000 to 1,500 post-transplant Hodgkin lymphoma patients who might be eligible for treatment with Adcetris if regulators approve expanded use based on the AETHERA results.
Through the first nine months of the year, net sales of Adcetris in the U.S. totaled $132 million, up 25% year over year. Seattle Genetics' guidance calls for Adcetris U.S. sales this year to reach the range of $172-177 million, which represents about a 20% increase over 2013 U.S. net sales of $145 million.
Despite an improved outlook for Adcetris, Seattle Genetics' shares are down about 7% in what is otherwise a very strong year for biotech stocks. The main problem is the company's market value of almost $4.7 billion assumes far more Adcetris revenue than is currently being generated. Seattle Genetics believes Adcetris sales will grow significantly based on expanded use in Hodgkin lymphoma and the company is developing other cancer drugs. But investors have already given Seattle Genetics a lot of credit for future revenue. Some investors believe the lack of a survival benefit in the AETHERA study may dissuade doctors from using the drug as a maintenance therapy.
Adcetris may also come under competitive pressure from a new class of cancer immunotherapy known as checkpoint inhibitors. Later at this ASH meeting, early studies of Merck's (MRK) Keytruda and Bristol-Myers Squibb's (BMY) Opdivo in Hodgkin patients no longer responsive to Adcetris are being presented. The results, some of which were disclosed in November, were very strong.
Hodgkin lymphoma is a cancer caused by the unchecked growth of white blood cells in the lymphatic system. These wildly multiplying cells can then invade other parts of the body. Most patients with newly diagnosed Hodgkin lymphoma can be treated successfully with chemotherapy or a stem-cell transplant.
Adcetris is an "antibody-drug conjugate" consists of an antibody that attaches itself to a certain protein receptor found on Hodgkin cells. Once inside the tumor, Adcetris releases a toxic chemotherapy payload to kill the cells.