BREAST CANCER

STAGES

The stage of a breast cancer provides information about how advanced the cancer is, i.e to what size and shape it has grown (at the time of diagnosis) and whether it has metastasized (i.e. some of its cells have split from the main lump and traveled through the blood or lymphatic vessels to distant parts of the body, where they have started growing). The most commonly used staging system, developed and last updated in 2018 by the American Joint Committee on Cancer (AJCC), is the TNM system, which looks at the size and shape of the tumor, whether it has spread to the lymph nodes, and whether the are metastases in remote areas of the body.

T(issue): What size and shape the tumor is, particularly whether it has grown
into surrounding healthy breast tissue (characteristics of the cancer local)
N(odes): Whether the cancer has spread to the nearby lymph nodes (characteristics of the cancer regional)
M(etastases): Whether the cancer has spread to remote, distant parts of the body (characteristics of the cancer in the whole body)

Based on these characteristics, 5 stages have been developed (Stage 0-IV), with a higher stage number indicating a more advanced disease. While the exact science of staging a breast cancer is complex and intricate (there are several sub-stages!), often depends on the interplay of a variety of factors, and can only be done by a treating physician with knowledge of both the patient history and tumor histology, a rough approximation of the staging system can be broken down as follows.

Stage 0 ("in situ"): The cancer is small and has not grown beyond the immediate structure from which it grew (i.e. the lobule or duct)
Stage I: The cancer is still relatively small, but it has grown beyond its immediate origin into surrounding breast tissue, usually fatty, connective or or muscle tissue surrounding the glandular (milk producing and transporting) structures.
Stage II: The cancer reaches or exceeds 2 cm in diameter and may have spread to some (few) close by lymphatic structures, such as the axillary lymph nodes.
Stage III: The cancer reaches or exceeds 5 cm in diameter and/or can be found in several (many) close by lymph nodes and/or the cancer has grown so large that it breaks through the skin and forms an ulcer.
Stage IV: The cancer has metastasized (spread) to distant organs of the body, often the brain, the lungs, or the bones.

While Luminal A type breast cancer often remains at Stage 0-I, Luminal B type breast cancer and especially the more aggressive HER2-positive and Basal-type (triple negative) breast cancers tend to progress rapidly to more advanced stages.