One of the primary complications of bone marrow transplantation is called graft vs. host disease (GVHD), in which the donor's healthy stem cells see the recipient as foreign — a kind of reverse rejection — and react, sometimes badly. Common sites for acute GVHD include the skin, stomach and liver. The good news, Petersen said, is GVHD usually burns out over time, although it can take several years. Asch said, on average, 15 percent of transplant patients are being teated for GVHD at the two-year point following the transplant.

GVHD is often even desirable. You want some of it for certain cancers, they said, because of a graft vs. cancer effect. The same reaction to the recipient's normal cells is amplified against cancer cells, which are anything but normal, and can successfully kill any lingering cancer cells. Patients who experience GVHD are less likely to have a recurrence of the cancer.

Donating bone marrow is not a particularly tricky or risky process. Petersen said they often schedule bone marrow donations for Thursday, because most people will be able to go back to work on Monday. The marrow is taken through four tiny holes in the patient's lower back. It's very uncommon for a donor to require hospitalization. The most common side effects are a back ache and residual fatigue until the marrow replenishes itself.

And they warn donors to be aware of their feelings. Particularly if the recipient doesn't do well with the transplant, there's a tendency for donors to feel like they somehow are to blame. When they see someone struggle with GVHD, some feel guilty. In reality, said Petersen, "after the cells are in (the other person), it's out of their control."

The hotline tackles a different health topic on the second Saturday of each month.

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E-mail: lois@desnews.com