Infiltrating lobular carcinoma of the breast. Clinicopathologic analysis of 975 cases with reference to data on conservative therapy and metastatic patterns.

BACKGROUND: The clinicopathologic features of infiltrating lobular carcinoma (ILC), which represents 5% to 15% of all breast cancers, are still controversial. In particular, the high frequency of multicentric lesions has led to questioning of the effectiveness of conservative treatment for this type of cancer. By studying a large number of cases, we aimed to compare the clinicopathological features of ILC with those of nonlobular infiltrating carcinoma (NLIC) and to assess the advisability of conservative therapy in the management of ILC.

METHODS: The population analyzed included 726 cases of ILC, 249 cases of mixed ILC/invasive ductal carcinoma (ILC/IDC), and 10,061 cases of NLIC. The age of patients, TNM status, estrogen- and progesterone-receptor status (ER, PR), and histologic grades of the 3 groups were compared. The follow-up was carried out on a subgroup of 5846 cases.

RESULTS: At diagnosis, ILC tumors were found to be larger on average and were detected in patients older than those with NLIC, but the degree of lymph node involvement was lower in patients with ILC than in NLIC. In ILC, tumors are more frequently grade I and ER-positive than in NLIC. Multicentric lesions were not significantly more frequent in ILC than in NLIC. The overall survival, locoregional control, disease free interval, and metastatic spread rates were not different among the three groups neither by univariate nor multivariate analysis, but the pattern of metastatic dissemination was different. In 480 cases of ILC considered for conservation therapy, the local recurrence and overall survival rates were similar to those observed for IDC.

CONCLUSIONS: Our analysis specifies the clinicopathological features of ILC and confirms that conservation therapy may be an appropriate treatment for this type of cancer.