RISK OF BREAST-CANCER SUBSEQUENT TO HISTOLOGICAL OR CLINICAL-DIAGNOSIS OF FIBROADENOMA - RETROSPECTIVE LONGITUDINAL-STUDY OF 3938 CASES

Background: The widespread belief that fibroadenoma is associated with an increased risk of subsequent breast cancer is based on studies of histologically-confirmed fibroadenomas. In current practice only a min ority of fibroadenomas are excised: most of them are diagnosed on the basis of palpation and imaging, and are not surgically removed. The de cision for surgical excision may be influenced by the presence of indi vidual risk factors, and this can act as a confounder and bias studies that are based only on surgically excised fibrodenomas.Patients and m ethods: To investigate this hypothesis we linked data from a consecuti ve series of 3938 fibroadenomas diagnosed histologically (n = 1335) or clinically (n = 2603) in women aged 30 to 69 years to the Tuscany Can cer Registry database. After exclusion of concurrent breast cancers or cancers occurring within six months after the diagnosis of fibroadeno ma, the observed and expected incidence of subsequent breast cancer we re compared. Results. The overall Standardized Incidence Ratio (SIR) f or excised and non-excised fibroadenomas was 1.38 (95% CI = 1.1-1.7). The SIR for histologically-confirmed fibroadenomas was 2.0 (95% CI 1.4 -2.7) whereas there was no apparent risk for non-excised fibroadenomas (SIR = 0.97, 95% CI = 0.7-1.4). Conclusion. This study suggests that assessment of breast cancer risk subsequent to a diagnosis of fibroade noma may be biased if the analysis is limited to surgically-excised fi broadenomas.