INVASIVE (INFILTRATING) LOBULAR CARCINOMA

Invasive lobular carcinomas constitute the second most frequent type of invasive breast cancer. In most series, these tumors account for 5% to 10% of invasive breast carcinomas.   However, the reported incidence of this tumor type has ranged from under 1% to as high as 20%. Some of this difference may be related to differences in patient populations. Most of this variability, however, appears to be related to differences in diagnostic criteria. In particular, since the time the classic form of invasive lobular carcinoma was described by Foote and Stewart, a variety of authors have described invasive breast cancers that they consider variants of invasive lobular carcinoma, thereby expanding the spectrum of this histologic type and accounting for a higher incidence of invasive lobular carcinoma in more recent series than in the past.

Invasive lobular carcinomas are characterized by multifocality in the ipsilateral breast and appear to be more often bilateral than other types of invasive breast cancer, although the reported range of bilaterality has been broad (6% to 47%). In two clinical follow-up studies of patients with invasive lobular carcinoma, however, the incidence of subsequent contralateral breast cancer among patients with invasive lobular carcinoma was similar to that of patients with invasive ductal carcinoma.

Lobular carcinoma in situ coexists with invasive lobular carcinoma in the majority of cases. Overall, 70% to 80% of cases of invasive lobular carcinoma contain foci of lobular carcinoma in situ.

Clinical Presentation

Invasive lobular carcinoma may present as a palpable mass or a mammographic abnormality with characteristics similar to those of invasive ductal carcinomas (i.e., discrete, firm mass on palpation; spiculated mass on mammogram). The findings on physical examination and the mammographic appearance in some cases of invasive lobular carcinomas may be quite subtle, however. Physical examination may reveal only a vague area of thickening or induration, without definable margins. Mammographic findings may be equally subtle, with many invasive lobular carcinomas appearing as poorly defined areas of asymmetric density with architectural distortion, and others revealing no mammographic abnormalities, even in the presence of a palpable mass. In fact, the extent of the tumor may be substantially underestimated by both physical examination and mammography.

Gross Pathology

Some invasive lobular carcinomas appear as firm, gritty, grey-white masses, indistinguishable from invasive ductal carcinomas. In other cases, however, no mass is grossly evident, and the breast tissue may have only a rubbery consistency. In still other cases, no abnormality is evident on visual inspection or on palpation of the involved breast tissue, and the presence of carcinoma is revealed only on microscopic examination.

Clinical Course and Prognosis

Several aspects of the clinical course of invasive lobular carcinomas merit consideration. First, a number of studies have noted differences in the pattern of metastatic spread between invasive lobular and invasive ductal carcinomas. In particular, metastases to the lungs, liver, and brain parenchyma appear to be less common, and metastases to bone more common, in patients with lobular cancers than in those with ductal cancers.   Furthermore, lobular carcinomas have a greater propensity to metastasize to the leptomeninges, peritoneal surfaces, retroperitoneum, gastrointestinal tract, and reproductive organs. In fact, the majority of cases of carcinomatous meningitis in patients with metastatic breast cancer occur in patients with lobular cancers. Peritoneal metastases may appear as numerous small nodules studding the peritoneal surfaces in a manner similar to that seen in ovarian carcinoma. Metastases to the stomach can produce an appearance that simulates an infiltrative (linitis plastica) type of primary gastric carcinoma. Involvement of the uterus may result in vaginal bleeding,  whereas a metastatic tumor in the ovary may produce ovarian enlargement and the appearance of Krukenberg's tumor.

Whether invasive lobular carcinomas differ in overall prognosis from invasive ductal carcinomas is difficult to determine, due in large part to variations in the application of histologic criteria for the diagnosis of invasive lobular carcinoma. However, the prognosis of patients with invasive lobular carcinoma as a group has not consistently been shown to differ from that of patients with invasive ductal carcinoma.  Several studies have suggested that the prognosis for the classic form of invasive lobular carcinoma is better than that for the solid variant,  and that the tubulolobular variant has a particularly favorable prognosis.  However, attempts to assess prognostic differences between classic and variant forms of invasive lobular carcinoma have been limited by the small numbers of patients in the variant subgroups in virtually all of the published series and by the failure in some series to stratify patients by stage, and the results across studies have been inconsistent. Some studies have suggested that the classic form of invasive lobular carcinoma is associated with a more favorable prognosis than is invasive ductal carcinoma.  In the study of DiCostanzo et al., however, a prognostic advantage for invasive lobular carcinomas over invasive ductal cancers was seen only among patients with stage I disease.  Available evidence suggests that the pleomorphic variant  and the signet-ring cell variant (when defined as lesions in which more than 10% of the neoplastic cells are of the signet-ring cell type)  appear to be associated with a particularly poor clinical outcome.

Numerous clinical follow-up studies have indicated that patients with invasive lobular carcinoma can be adequately treated with conservative surgery and radiation therapy after a complete gross excision of the tumor; local recurrence rates are comparable to those seen in patients with invasive ductal carcinoma.