A retrospective study of women diagnosed with breast cancer from 1975 to 1999 suggests that a trend toward detection of smaller tumors over those 25 years contributed to the improved 5-year survival rates during that period, according to a study published online August 8 in Cancer.

Researchers at Memorial Sloan-Kettering Cancer Center, led by Dr. Elena Elkin, reviewed data from NCI's Surveillance, Epidemiology, and End Results (SEER) program for women initially diagnosed with nonmetastatic breast cancer with tumors that were either localized (limited to breast tissue) or regional (limited to nearby tissue or lymph nodes). More than 265,000 tumors were analyzed.

"Within each stage category, the proportion of smaller tumors [detected] increased significantly over time," the researchers noted. For example, the localized tumors smaller than 1 cm accounted for only 10 percent of patients diagnosed between 1975 and 1979, compared with 25 percent of localized breast cancers detected between 1995 and 1999. Similarly, among women with regional disease, the number of tumors found smaller than 2 cm increased from 20 to 33 percent during the same comparison periods.

"Comparing patients diagnosed between 1995 and 1999 with those diagnosed between 1975 and 1979, within-stage migration of tumor size accounted for 61 percent and 28 percent, respectively, of the relative survival increases noted in localized and regional breast carcinoma," the researchers concluded. In contrast, 5-year survival rates for same-size tumors "changed by much smaller amounts during the 25-year period," they added.

The trend toward increased breast cancer survival in the United States over the past three decades has been attributed to advances in both screening and treatment. For example, the first national mammography screening guidelines were issued in the late 1970s. "But distinguishing the relative contributions of these two modalities is difficult," the researchers noted. The researchers chose to examine tumor size as "an obvious marker of natural history and a strong predictor of breast carcinoma survival."

The impact of smaller tumor sizes at diagnosis was especially significant for women aged 65 and older in the study. Among the localized breast cancer patients, smaller tumor size accounted for 96 percent of observed improvement in relative survival for that age group. The researchers observed that "In regional breast carcinoma cases, tumor size standardization explained twice the proportion of survival benefit in women age 65 and older (44 percent) compared with women ages 25-49 years (23 percent) and 50-64 years (22 percent)."

A note of caution on the limitations of the study was voiced by Dr. Jo Anne Zujewski, head of NCI's Breast Cancer Therapeutics in the Clinical Investigations Branch: "While a smaller tumor size at diagnosis undoubtedly contributes to some of the survival improvement noted, clinical trials have clearly demonstrated survival improvements due to treatment in all early stages of breast cancer. So we remain convinced that the improved outcomes noted over time result from a combination of detection and treatment factors."

By Bill Robinson