Summary: BACKGROUND: The efficacy and reproducibility of mammographic tumour feature use for predicting patient outcome were tested in consecutive in situ and 1-14 mm invasive breast cancer cases from two breast centres in two different health care systems. METHODS: All in situ and 1-14 mm invasive cancers detected in Falun from 1996-2006 (n ≥ 971), in Roanoke from 2002-2007 (n ≥ 555), and in women aged 40-69 (age limits for invitation to screening) in Falun from 1977-1995 (n ≥ 844) were included; of these the mammograms, pathology slides and follow-up information were available in 95%, 97% and 91% of the cases, respectively. The cancers were classified according to their mammographic appearance: stellate or circular without associated calcifications, or malignant type calcifications with or without an associated tumour mass. The mammographic tumour features and the disease specific survival were correlated. Terminal digit preference of tumour size measurements was examined. RESULTS: Mammographic tumour features were similarly represented in both centres. A significant preference was observed for tumour size measurements divisible by 5 mm. Outcome was significantly poorer for cases having casting type calcifications on the mammogram and excellent for the remaining cases. CONCLUSIONS: Outcome prediction of patients with 1-14 mm invasive breast cancer is significantly improved by the addition of mammographic tumour features to the currently used prognostic factors. The integration of imaging morphology into the TNM classification of invasive breast cancers smaller than 15 mm facilitates specifically targeted therapy and may curtail overtreatment. The significant digit preference found in this study may justify using the terminal digits of "4" and/or "9" as upper size limits for tumour size categories.
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