Impalpable breast lesions diagnosed by mammography: incidence of histologically confirmed malignancy.
OBJECTIVE: To evaluate the suitability of currently applied mammographic criteria for the early diagnosis of subclinical tumours by comparing radiological findings with the final histological diagnosis. DESIGN: Open study. SETTING: District hospital, Denmark. SUBJECTS: 151 Women who underwent needle biopsy of 161 occult breast lesions that had been diagnosed by mammography during the period 1986-90. INTERVENTIONS: Definitive operation if frozen section at the time of needle biopsy indicated malignancy. Radiographic examination of the specimen ensured that the abnormal area had been excised. MAIN OUTCOME MEASURES: Correlation of mammographic and histological findings. RESULTS: Eight foci showed carcinoma in situ and 33 invasive carcinoma; 10 of the 33 had lymph node metastases. Foci with mammographic masses had a significantly higher risk of malignancy than those without (25/70, 37%, compared with 8/91, 17%, p = 0.005). Spiculated foci with clustered calcifications had the highest risk of malignancy (6/11, 54%). 16/87 foci in women less than 50 years old contained malignant disease compared with 25/74 in women aged 50 or more (p = 0.04). A fifth of the frozen sections contributed nothing to the diagnosis. The incidence of malignant disease in impalpable lesions of a quarter is similar to the reported incidence in palpable mammary tumours, but metastases at the time of diagnosis are appreciably less common (30% compared with 50%). CONCLUSION: The currently applied mammographic criteria are particularly helpful to patients under the age of 50.