Back at the time when the group, which included CIRM grantee Irv Weissman, carried out this trial, doctors were rejecting high-dose chemotherapy for people with metastatic breast cancer. That therapy destroys the cancer, but also destroys the patient's bone marrow, which produces all blood and immune cells. That side effect would be deadly, but doctors can reinject bone marrow cells taken from patients before chemotherapy. This is the process that is used today for many types of cancers. However, doctors were finding that the whole bone marrow also contained some breast cancer cells. If those cells survived the transplantation they could spread and form a new, deadly cancer. So much for the chemotherapy.
Back when the Stanford scientists carried out their trial (between 1996 to 1998) Weissman had recently figured out how to purify the blood-forming stem cells in the bone marrow that are responsible for rebuilding the blood system. He and the team thought they could pull out just those cells from the patient's blood and use those cells to save the blood system after high-dose chemotherapy. If it worked, the chemotherapy would destroy the cancer, and the purified stem cells would save the blood system without reintroducing cancer cells lurking in the blood.
It all sounded good, but they were not sure whether their idea had worked until now. What they learned is that 23 percent of the women in their trial are still alive, compared to 9 percent of women who received unpurified stem cells.
A Stanford press release about the work quotes Weissman:
“Even with this small sample size, this paper demonstrates much-better overall and progression-free survival in those patients who received cancer-free stem cells.”Senior author on the paper Judith Shizuru said in the release:
“Most people in the oncology community feel that this issue is a done deal, that high-dose chemotherapy does not work for patients with breast cancer. But our study suggests that the high-dose therapy strategy can be modified to include the use of cancer-free purified blood stem cells to yield better overall outcomes in women with advanced breast cancer.”The authors are encouraging scientists to revisit high-dose chemotherapy for other cancers where it isn't traditionally offered. If it shows benefit for those patients it could open up a new form of therapy for a wide range of cancers.
This paper also highlights something that will continue to be true of all forms of stem cell research: It takes a long time to learn whether a therapy was truly effective. A decade from now we'll know whether the stem cell trials of today really worked. It's slow and frustrating, but papers like this one make the wait worth while.