INVASIVE LOBULAR CARCINOMA OF THE BREAST - MAMMOGRAPHIC FINDINGS AND EXTENT OF DISEASE AT DIAGNOSIS IN 184 PATIENTS

OBJECTIVE. Invasive lobular carcinoma of the breast is a distinct malignant neoplasm consisting of small cells that tend to infiltrate in thin strands that are often only one cell in width. The objectives of this study were to determine if these tumors are more frequently overlooked on mammograms than are other types of invasive carcinoma and to evaluate the specific mammographic and pathologic findings of this disease at the time of diagnosis. MATERIALS AND METHODS. From 1983 through 1991, invasive, purely lobular carcinoma of the breast was diagnosed in 184 women who had screen-film mammography and biopsy at our institution. We examined the initial mammographic reports to determine the principal abnormal mammographic findings that supported or prompted biopsy and to distinguish abnormalities that were overlooked in breasts with false-negative mammographic findings. All mammograms were retrospectively examined for benign or suspicious microcalcification in the vicinity of the neoplasm and for breast parenchymal patterns. Surgical pathology reports were also reviewed. RESULTS. The rate of false-negative findings on initial interpretations of mammograms was 19%. Forty-six percent of the mammograms with false-negative initial interpretation showed no evidence of malignant tumor in retrospect. Ten percent of the neoplasms showed suspicious calcification on mammograms, and 1% of patients had biopsy primarily because of worrisome calcification. Invasive lobular carcinoma tends to produce masses that are of relatively low radiographic opacity, similar to normal fibroglandular breast tissue. Forty-four percent of patients had metastases to axillary lymph nodes at the time of diagnosis. One patient had bilateral invasive lobular carcinoma. CONCLUSION. Our results show that the false-negative rate for the diagnosis of invasive lobular carcinoma is higher than that for other invasive cancers. The reasons for this difference appear to be the low rate of suspicious calcification found with invasive lobular carcinoma and its tendency to be of low opacity. We also found a lower rate of bilateral invasive lobular carcinoma than has been generally reported. Metastases to lymph nodes were common at the time of diagnosis.