Better treatments for certain aggressive prostate cancers may stem from the targeting of a specific protein on the surface of some prostate cancer cells, according to a new study.
In the study, drugs that targeted the protein, which is called SPINK1, shrank prostate cancer tumors in mice by 74 percent.
One of the drugs, cetuximab, is already approved by the Food and Drug Administration to treat head and neck cancer and colorectal cancer, so clinical trials to test its effectiveness in specific cases of prostate cancer could be conducted fairly rapidly, said study researcher Scott Tomlins of the University of Michigan Medical School.
Ten percent of prostate cancers contain cells with SPINK1 on their surfaces, so the treatments, if proven effective, would work only in those cases.
The research reflects how researchers are increasingly focusing treatments on subtypes of cancers, rather than viewing prostate or any type of cancer as a uniform disease, Tomlins said. "The paradigm of cancer treatment is sort of shifting," Tomlins said. "Instead of treating all patients blindly, it's really looking at … the specific molecular alterations that that patients' cancer has."
The study is published today (March 2) in the journal Science Translational Medicine.
Previous work by Tomlins and colleagues associated SPINK1 with aggressive prostate cancer. The protein may drive cancer cells to divide and metastasize, Tomlins said.
In the new study, the researchers said they treated the mice with an antibody that binds specifically to SPINK1 and found that the tumors shrank by 60 percent.
Next, they tested cetuximab. The drug binds to a protein found on cell surfaces called EGFR, which is known to interact with SPINK1. Tumors treated with cetuximab shrank by 40 percent.
Mice treated with both the antibody and cetuximab saw their tumors shrink by 74 percent.
Earlier clinical trials tested cetuximab as a treatment for prostate cancer. But because the results were so poor — only 8 percent of patients showed a benefit — there wasn't any follow-up of the drug. The researchers hope future clinical trials will examine the outcome specifically for patients with SPINK1 present on their cancer cells, Tomlins said.
The new findings mean it might be possible to stratify prostate cancer patients according to which treatment they will respond to, as is currently done for breast cancer , said Amina Zoubeidi of the Vancouver Prostate Centre in Canada. The drug Herceptin will work for breast cancer patients only if their tumors express the HER2 receptor.
Even if a drug worked for only 10 percent of prostate cancers, it would be a good start, Zoubeidi said.
"It's a significant number for your father or your husband or your son who has prostate cancer," Zoubeidi said.
If more drugs are developed that target other subsets of the population, it may be possible to treat 60 or 70 percent of patients, she said.
Pass it on: Targeting the protein SPINK1 on the surface of prostate cancer cells might reduce tumor growth in certain cases.
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