There are different subtypes of invasive lobular carcinoma (ILC) that are based on how the cancer cells look under the microscope. In its most typical or “classic” form, ILC is made up of small cancer cells that invade the stroma. The stroma includes the fatty tissue and ligaments that surround the ducts and lobules and also surrounds the blood and lymph vessels in the breast. Classic ILC cells tend to invade the stroma one-by-one in a single-file pattern. The cancer cells generally look quite similar to each other. The nuclei, or cores of each cell containing genetic material, tend to be small and look alike from cell to cell.
If the cancer cells grow in a different pattern than classic ILC — that is, not in a single-file formation — you may hear your doctor refer to one of these subtypes of invasive lobular carcinoma:
- Solid: The cells grow in large sheets with little stroma in between them.
- Alveolar: The cancer cells grow in groups of 20 or more.
- Tubulolobular: This subtype has some of the “single-file” growth pattern of classic invasive lobular carcinoma, but some of the cells also form small tubules (tube-like structures).
If the cancer cells themselves look different from classic invasive lobular carcinoma cells, you may hear your doctor refer to one of these subtypes:
- Pleomorphic: The cancer cells are larger than they are in classic ILC, and the cells’ nuclei look different from each other.
- Signet ring cell: In this type of ILC, the tumor contains some cells that are filled with mucus that pushes the nucleus (the core of the cell that contains genetic material) to one side. Because of their appearance, these cells have come to be known as signet ring cells.