The findings, which are being reported in The New England Journal of Medicine, show that the virus can rapidly mutate in certain patients to become Tamiflu resistant.
Only months before, a new drug had shown that it could safely slow the cancer's progress in certain patients.
These agents can cause edema (fluid accumulation in tissues), liver toxicity, and adverse cardiovascular events in certain patients.
An independent Food and Drug Administration advisory panel said yesterday that there was adequate evidence to support approving a Merck blood pressure drug, Cozaar, for reducing the risk of stroke in certain patients.
He added that next year, a group of experts he leads in the American Society of Clinical Oncologists will issue guidelines calling for more use of colony stimulating factors in certain patients to help them tolerate full-strength chemotherapy.
"We sent the letter to oncologists to heighten their awareness and educate them about infrequent adverse events that can occur in certain patients," said Neil Cohen, a spokesman for Genentech.
Even when agency officials warn against the use of drugs in certain patients, some doctors prescribe them dangerously anyway and patients die.
That marked a radical difference from standard chemotherapies, whose reason for working in certain patients and not others is not well understood.
The newer metal-on-metal hip implants, for instance, are somewhat controversial and may cause tissue and bone damage in certain patients.
"These events do not lead to death in all patients but can get compounded in certain patients who have poor general condition and nutritional status".
In certain patients radiation therapy may be utilized to eradicate the tumor and allow organ preservation.
