Cancer: Advance Against Leukemia

Physicians who deal with leukemia are reluctant to talk in terms of "breakthroughs" and "cures." Their fundamental position is that acute leukemia, the most common killing disease among children aged three to 14, is still fatal. With that reservation, however, a group of first-rank U.S. medical researchers met in Boston last week to discuss a series of remarkable gains that are now giving leukemia victims progressively longer survival times with greater comfort. In a few cases, they reported complete freedom from evident disease for as long as 15 years. In cautiously double-negative terms, they admitted that they could not be sure that they did not have a cure for some patients.

Only 20 years ago, the victim of acute leukemia could expect to live, on the average, from four months to a year after his disease was diagnosed.

Many doctors tended to give as little treatment as possible to avoid prolonging the patient's suffering. But Dr. Sidney Farber of the Children's Hospital Medical Center in Boston was just then beginning the first tentative treatment of childhood leukemia with a drug called methotrexate that interferes with the metabolism of cancerous cells, in effect starving them of a vital nutrient. It was to commemorate the 20th anniversary of that occasion that the American Cancer Society and the National Cancer Institute picked Boston as the place to make their reports last week.

Ten-Log Kill. When it came to pin pointing the causes of leukemia, the researchers were still at a loss. But there was no doubt about effects. The National Cancer Institute's Dr. C. Gordon Zubrod reported that by the time a leukemia patient is ill enough for his disease to be diagnosed, he usually has 1012 (or 1 trillion) leukemic cells in his blood. His physician must try to kill all these abnormal cells without killing or damaging too many of the normal cells. In the trade, said Dr. Zu brod, each factor of ten in that trillion cells is called a log, and in the first few years after Dr. Farber introduced methotrexate treatment, doctors found that they could knock off one or at most two logs, or zeros, from the cell count. This meant that more patients enjoyed longer remissions. Survival times began to creep up.

In 1953, Manhattan's Sloan-Kettering Institute introduced another anti-leukemia drug, 6-mercaptopurine. Use of the two drugs in succession, along with prednisone (a cortisone-type hormone) raised the kill to three to five logs. Since 1963, with half a dozen new anti-leukemia drugs available for concurrent or consecutive use, the cell kill achieved in the best cancer centers has reached ten logs, reducing the leukemic-cell count to 100.

Since even these few cells can multiply and cause relapses, the obvious objective is a twelve-log kill—the elimination of every last leukemic cell. And the ultracautious Dr. Zubrod made what is, for him, a wildly optimistic statement: "I believe that in about 25% of patients with acute lymphocytic leukemia now starting treatment, the cell kill is approaching twelve logs."*