Breast cancer is not a single disease but many different diseases. The evolution of breast cancer is divided into five stages. The stage indicates how far the tumor has spread from the original site. It is the most frequent type of cancer that is found in the female. Differences affect survival rates.
Breast cancer can be cataloged in different ways. From a morphological (or histological) point of view, it is possible to distinguish which type of cells give rise to the tumor, the cells of the lobules (the small glands responsible for the production of milk) or of the milk ducts (which, as the name says, carry milk from the lobule to the nipple). The most frequent type of tumor is ductal carcinoma, followed by lobular carcinoma.
Depending on their ability to invade other tissues than the one from which they originated, tumors can be described as "non-invasive" or "invasive." Both ductal and lobular carcinoma can occur in the non-invasive (in situ, abbreviated with the abbreviations DCIS and LCIS, respectively), or invasive (infiltrating) form, much more dangerous because it is capable of affecting distant organs. It is important to remember that today LCIS is considered in all respects a benign lesion and no longer a carcinoma.
From the point of view of its evolution, the tumor is classified into five categories or stages:
This category includes carcinomas, lobular, and ductal, non-invasive (in situ); both represent a high-risk factor for aggressive forms of cancer. Five-year survival is 98%, although relapses are possible.
It is the initial stage; carcinomas with a diameter of fewer than 2 centimeters and which have not yet involved lymph nodes are classified as stage I. Most often, it is necessary to perform a quadrantectomy (i.e., the removal of about a quarter of the breast). In these cases, after surgery, it is necessary to undergo radiation therapy. When the tumor, although small, is present in several locations or particular risk factors are present, a mastectomy must be performed. In this case, radiation therapy is not necessary. Sentinel node biopsy is always provided for stage 1 tumors. The 5-year survival rates for breast cancer identified in stage 1 are close to 100 percent.
It is always an early-stage tumor. This category includes carcinomas larger than 2 centimeters (up to 5 centimeters) that have not yet reached the axillary lymph nodes, or the smaller ones in which; however, the lymph nodes have already been involved. Tumors in which malignant cells are not in the breast but only in the axillary lymph nodes also fall into this category.
The tumor measures between 2 and 5 centimeters and has already spread to the lymph nodes or is larger than 5 centimeters but has not yet reached the lymph nodes.
It is a tumor with variable dimensions that has reached the axillary lymph nodes (often fused together) or involved other tissues close to the breast.
The tumor has reached the chest wall, ribs, or skin.
The tumor has reached the lymph nodes under the clavicle and near the neck and may have spread to those inside the breast and under the arm, and in the tissues close to the breast. This tumor is defined locally advanced.
It is the metastatic stage, in which the carcinoma has spread to organs other than the breast.
There is also another classification system, called TNM, T indicates the tumor size on a scale of 1 to 4 (T1-T4); N indicates whether or not the lymph nodes adjacent to the tumor have malignant cells (N0: they are not present; N1: they are present); M indicates the presence or absence of metastases (M0: no metastases are present; M1: metastases are present).
Breast cancer is classified into different "types" also on the basis of some of its molecular characteristics. In particular, it is based on the receptors present on its cells. Receptors are proteins that are found on the cell membrane and that bind to certain hormones produced by the body, with a "key-lock" mechanism; this process activates the cell, promoting its multiplication.
Together with the stage, the quantity of receptors is used by doctors as a prognostic indicator: the more there are (overexpression), the more cancer will tend to grow and evolve quickly. This classification, therefore, helps to estimate the rate of growth of the carcinoma and the probability that it will spread to other organs, that it will respond to certain treatments, or that, once eliminated, it can reappear.
Based on the receptors, invasive carcinomas are called HR-positive (from hormone receptors) if they have many receptors for female hormones - and can be estrogen-positive (ER +) and progesterone-positive (PR +). Overall, around 70% of breast cancer cases are hormone-responsive. This subgroup is further distinguished in "luminal carcinomas A" (neoplasms with the expression of hormone receptors with favorable prognosis) and "luminal carcinomas B" (neoplasms that, although they possess the expression of hormone receptors, present a high risk of recurrence).
On the other hand, tumors with many type 2 receptors of the human epidermal growth factor are called HER2 positive (from human epidermal growth factor receptor 2) (breast tumors can be HR and HER2 positive at the same time). This type of neoplasm represents about 20% of cases.
Carcinomas that do not have any of the three receptors are the fourth subtype, commonly called "triple negatives." They represent about 15% of cases. Some of these tumors are less aggressive than the three previous subtypes, while others are particularly aggressive and often recur, depending on whether they are non-basal or basal. In most cases, patients with non-basal type tumors have a lower risk of disease recovery and a better prognosis. Possible molecular targets are currently being studied to develop new drugs, including immunotherapy.