The second type is called lobular carcinoma in-situ, or LCIS, and that's where clusters of tumor cells grow within the lobules, without invading the ducts, causing the affected alveoli to enlarge.
Breast cancer usually begins as an in-situ carcinoma, which can either be ductal carcinoma in-situ, or DCIS, which is localized to the ducts, or lobular carcinoma in-situ, or LCIS, which is localized within the lobules.