Smaller tumors aid survival chances

Much of the improvement in breast cancer survival in recent years is because the average tumor is smaller, not just because treatments are so much better, a huge new study has found.

Examining 25 years of cancer records nationwide, researchers concluded that smaller tumor size accounted for 61 percent of the improvement in survival when cancer had not spread beyond the breast and 28 percent when it had spread just a little.

For women 65 and older with early-stage tumors – the most common scenario – the shift in size accounted for virtually all of the improvement in survival.

“We don’t in any way want to diminish the benefits we’ve seen from advances in treatment because they’ve been enormous,” said lead researcher Elena Elkin. “But not all of the improvement in survival is due to treatment when important characteristics like size also have changed over time.”

The study wasn’t designed to determine the value of mammograms or treatments. But it implies much about the value of early detection.

“This really helps to show the importance of screening,” said Debbie Saslow, who heads breast cancer research at the American Cancer Society. “In addition to finding more small tumors, we’re also finding fewer big tumors.”

Saslow had no role in the study, which is being published today online by the society’s journal Cancer and will appear in its Sept. 15 print edition.

It was conducted by doctors at Memorial Sloan-Kettering Cancer Center in New York and used a federal government database that includes nine cancer registries covering 10 percent of the U.S. population. More than 265,000 breast tumors were analyzed.

Survival has increased, but experts have argued over how much of that is because of better drugs or because of tumors being found at earlier stages. Two-thirds of breast cancer cases today are diagnosed at the local stage when they’re still confined to the breast; in the 1970s, only half were.

However, this is the largest study of American women to look at size within those stages.

“Even within the same stage category, the average tumor size is smaller today than it was 25 years ago,” Elkin said.

For example, the number of local-stage breast cancer tumors that were smaller than 1 centimeter rose from less than 10 percent from 1975 through 1979 to 25 percent from 1995 through 1999. An inch equals about 2.5 centimeters.

Of regional-stage cancers – those that had spread to nearby tissue or lymph nodes but not widely throughout the body – the portion that were smaller than 2 centimeters rose from one-fifth to one-third.

Researchers compared five-year survival rates for those time periods, taking into account the shift in tumor size.

For women with local-stage breast cancer, survival rose from nearly 91 percent to more than 97 percent but was only 93 percent after adjusting for smaller tumors. Looked at another way, the shift in size accounted for 61 percent of the improvement in survival.

For regional cancer cases, survival rose from about 68 percent to about 80 percent, but it was only 76 percent once tumor size had been factored in.

Size made a much bigger difference for older women than younger ones. A whopping 96 percent of the survival improvement for women age 65 and older with local-stage cancer was explained by this. Only 38 percent of the improvement in women under age 50 was due to the shift in tumor size.

“It isn’t necessarily because treatment works better for certain women – it reflects who’s getting more,” because younger women are more likely to receive chemotherapy, Elkin said.

It also shows that older women have benefited from mammograms, Saslow said.

However, Dr. Barnett Kramer, associate director for disease prevention at the National Institutes of Health, noted that the study did not have information on how many of the tumors were found through mammograms or what treatments various groups of women had received, so no direct conclusions about the value of them can be drawn.