Diagnosis, clinical staging, and treatment of breast cancer: a retrospective multiyear study of a large controlled population.

This study compares diagnosis, staging, and treatment of newly diagnosed breast cancer cases over a several-year period. The study design was a retrospective, multiyear comparison between new breast cancer cases diagnosed in 1995 (n = 827) and 1997 (n = 815). Cases were identified through claims data, and medical record abstraction was used to verify each case and to identify clinical staging and type of treatment. All medical records were reviewed by one physician to maximize internal reliability. Both cohorts were predominantly 40 and older, white, married, and postmenopausal. The latter cohort (1997) had a higher proportion of women aged 70 to 79 and a lower proportion of women aged 40 to 49. In both cohorts, women age 40 and older were likely to be diagnosed with breast cancer at the time of mammographic screening, while women younger than 40 were more likely to be diagnosed by clinical breast examination. In logistic regression analyses, controlling for confounding factors such as age, undergoing mammographic screening increased the likelihood of having a low cancer stage at diagnosis by more than three and a half times. Mammographic screening was statistically significantly positively associated with having eligibility for breast-conserving treatment (BCT); however, although an increase in BCT eligibility was observed, actual use of BCT did not change. Mammography leads to a lower clinical stage as well as a greater likelihood of BCT eligibility at time of breast cancer diagnosis, but may not have a substantial effect on treatment choice (lumpectomy vs. mastectomy). Between 1995 and 1997, a trend was observed toward downstaging of disease at diagnosis; further research is warranted to observe whether this trend continues over time.