Background: The widespread belief that fibroadenoma is associatedwith an increased risk of subsequent breast cancer is based on studies ofhistologically-confirmed fibroadenomas. In current practice only a minorityof fibroadenomas are excised; most of them are diagnosed on the basis ofpalpation and imaging, and are not surgically removed. The decision forsurgical excision may be influenced by the presence of individual riskfactors, and this can act as a confounder and bias studies that are based onlyon surgically excised fibrodenomas.
Patients and methods: To investigate this hypothesis we linked datafrom a consecutive series of 3938 fibroadenomas diagnosed histologically (n= 1335) or clinically (n = 2603) in women aged 30 to 69 years to theTuscany Cancer Registry database. After exclusion of concurrent breast cancersor cancers occurring within six months after the diagnosis of fibroadenoma,the observed and expected incidence of subsequent breast cancer were compared.
Results: The overall Standardized Incidence Ratio (SIR) for excisedand non-excised fibroadenomas was 1.38 (95% CI = 1.1–1.7). TheSIR for histologically-confirmed fibroadenomas was 2.0 (95% CI1.4–2.7) whereas there was no apparent risk for non-excisedfibroadenomas (SIR = 0.97, 95% CI = 0.7–1.4).
Conclusion: This study suggests that assessment of breast cancer risksubsequent to a diagnosis of fibroadenoma may be biased if the analysis islimited to surgically-excised fibroadenomas.