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Even the most enthusiastic proponents of interferon concede that it is a difficult substance to work with, far more complex than traditional anticancer drugs. Just getting the dosages right can be tricky, and they are different * with each disease. "More is not better with the interferons," says Mathilde Krim of New York City's Memorial Sloan-Kettering Cancer Center. "Giving too much can have the opposite of the desired effect."
Doctors suspect that interferon may be most effective not as a solo performer but in conjunction with other medications. "No single drug is the optimal treatment for any common cancer," says Dr. Ernest Borden of the University of Wisconsin. "The big question over the next five years will be how to combine interferons with other treatments." Particularly promising, says Borden, is combining several types of interferon, since one form seems to enhance the effects of another. Doctors are also excited about the possibility of using interferon together with another powerful, naturally occurring anticancer agent called tumor necrosis factor. "Interferon and TNF together add up to more than the sum of their parts," says Dr. Lloyd Old, of Sloan-Kettering, who discovered TNF 14 years ago. Interferon may work synergistically with certain cancer drugs and with radiation therapy.
Some of interferon's failings may stem from the fact that it has been tried mainly in the most desperate cases of cancer, on those for whom no other treatment has worked. "These are the worst possible conditions in which to test it," says Krim. She and others think that interferon holds greater promise for patients with early cancers and those whose immune systems have not been weakened by radiation treatment or chemotherapy. Other potential uses for interferon: heading off the recurrence of tumors after they have been surgically removed, and preventing precancerous conditions like cervical dysplasia from progressing into full-blown cancers. But much more testing lies ahead, says Dr. Ronald Herberman, chief of biological therapeutics at the National Cancer Institute, and the world will have to wait a bit longer to see what interferon can do. In the encouraging results so far, he says, "we may be seeing just the tip of the iceberg."