For women age 40 and older, annual screening mammography for breast cancer is more effective than infrequent or no mammography in detecting breast cancer at sizes and stages that yield excellent prognosis, according to results published in the journal Cancer.

The study also reveals that women who had annual screening mammograms were diagnosed at an earlier stage and with smaller tumors than women who had mammograms less often. Women who had annual screening mammograms were also more likely to be offered breast conservation therapy rather than mastectomy.

"This study supports many of the benefits associated with mammographic screening for women 40 years or older," conclude the authors, "and supports at least a yearly interval versus more than yearly for optimal detection of the most curable forms of breast cancer."

Routine screening mammography for breast cancer has been shown to have significant benefit to detect early primary breast cancer. The benefit is clear for women over 50 when breast tissue is less dense. But the data to support its use in women under 40 has been less clear.

In order to analyze the impact of various frequencies of screening mammography on tumor stage and size in women aged 40 and older, Freedman et al. reviewed data from 1,591 women diagnosed with primary breast cancer between 1995 and 2001. An average screening interval was estimated from each patients' age and their number or frequency of mammograms prior to their diagnosis of breast cancer.

The distribution of tumor stage showed a significant trend towards earlier stage disease in women who were screened annually. Approximately 26% of patients screened annually were diagnosed with the early form of breast cancer, ductal carcinoma in situ, compared with 21% of patients screened less often and 15% of patients with no prior screening.

Similarly, 56% of patients screened annually presented with stage T1 tumors (< 2-cm in diameter) compared with 50% of patients screened less often and 32% of patients with no prior history of mammography.

Furthermore, women with annual mammograms were more likely to be offered the option of treatment with breast conservation therapy. Approximately 61% of women with annual mammograms or less frequent mammograms were offered breast-conservation and 28% were recommended mastectomy. In contrast, 41% if women with no history of mammography were offered breast conservation therapy and 41% were recommended mastectomy.

"This study confirms a significant downstaging of tumor stage and tumor size associated with mammography screening [for women 40 years old] that has been shown in other recent studies as well," the authors conclude.

SOURCE:
Cancer, September 1, 2003