Which feature is indicative of Lobular Carcinoma in situ?

Lobular carcinoma in situ (LCIS) is characterized by its distinct biology and presentation, which includes its propensity for bilateral occurrence. This is significant because patients diagnosed with LCIS have an increased risk of developing breast cancer, especially in both breasts over time. The bilateral occurrence is linked to the multifocal nature of LCIS, meaning that it can simultaneously affect both breasts or be present in one breast and later develop in the other.

Other features listed, such as the presence of calcifications, can typically be associated with ductal carcinoma rather than lobular carcinoma. Extensive necrosis is more indicative of high-grade tumors that tend to be more aggressive, and while LCIS is a non-invasive condition, it doesn't typically present with necrosis. Furthermore, finding LCIS incidentally during pregnancy is not considered a central feature of the disease, even though certain types of breast lesions can be diagnosed during pregnancy due to increased surveillance. The hallmark feature of bilateral occurrence sets LCIS apart from other types of breast cancer and is a critical aspect of its risk profile and clinical management.