Abstract ED02-02: The Challenges of Lobular Carcinoma

Abstract Infiltrating lobular carcinoma (ILC) and lobular carcinoma in situ (LCIS) were first described in the1940s by two Memorial Hospital pathologists, Foote and Stewart. They were most intrigued by the infiltrative appearance of these lobular cancers which they described as demonstrating large numbers of isolated, loose or dyscohesive cells of rather uniform size but of varying shape. We now recognize that this dyscohesive growth pattern is the result of loss of a functional e-cadherin protein; a distinguishing feature between ILC and invasive ductal carcinoma (IDC). Several studies comparing clinical features and outcomes between ILC and IDC have generated consistent findings. Lobular cancers are more likely to be ER+, larger, lower grade, less likely to be detected on MMG and more likely to have positive margins at breast conserving surgery (BCS), or to require mastectomy. Yet importantly, if BCS is successful, local recurrence and rates of contralateral breast cancer are equal for ILC and IDC. Although lobular cancers represents only 5-15% of all breast cancer, numerically, if ILC was an independent cancer in women, it would rank as the 6th most common cancer in women. Notably the incidence of ILC rose sharply in the late 80s throughout the 90s, and it has become clear that there is a strong relationship between ILC and hormone replacement therapy. Perhaps the “strongest” risk factor for ILC, is LCIS. Classic LCIS is an incidental finding – there are no pathnogmonic features on breast imaging or gross examination of tissue. On microscopic examination it is often multicentric and bilateral. Although originally considered a precursor to ILC and treated with mastectomy, over the years it was realized that rates of ipsilateral cancer in women who were not treated for LCIS were lower than expected and were quite similar to rates of contralateral breast cancer – and this combined with the fact that only 50% of the cancers were of the lobular phenotype led to a movement to consider LCIS as a high risk lesion. Contemporary data continue to support this management approach as rates of cancer development in women with a diagnosis of LCIS are consistently reported at 1-2% per year and the risk is conferred bilaterally, with a slightly higher representation of ILC in the ipsilateral breast. In this presentation we will review areas of clinical controversy, including the use of MRI, the safety of breast conservation, the role of neoadjuvant chemotherapy and the utility of genomic assays in patients with ILC. Citation Format: T. King. The Challenges of Lobular Carcinoma abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr ED02-02.