Pink October: inflammatory, Paget's disease of the nipple… what are the different types of breast cancer ?

Octobre Rose : quels sont les différents types de cancer du sein ?

In 2023, more than 61,000 new cases of breast cancer were diagnosed. Each year, more than 12,000 women die from it. Ductal or lobular cancer, in situ or invasive, hormone-dependent or not… On the occasion of Pink October, we explain the different types and subtypes of breast cancer.

Breast cancer is by far the most common cancer in women. It represents more than a third of all new cases of cancer diagnosed. Stage, grade, triple negative, ductal… We are sometimes lost when we try to understand what breast cancer is, as there are so many names that can characterize it.

First of all, it is important to understand the anatomy of the breast. This organ is composed of supporting tissue that contains vessels, fibers and fat. It also contains a mammary gland, itself composed of 15 to 20 compartments separated by fatty tissue. Each compartment is made up of lobules and ducts. The ducts transport breast milk to the nipple, the lobules produce milk during breastfeeding.

Types of Cancer

There are different types of breast cancer depending on their histological type, that is, depending on the cells from which the cancer develops. The vast majority of breast cancers are adenocarcinomas (95%), they develop from epithelial cells (carcinoma) of the mammary gland (adeno) or a glandular epithelium. These carcinomas are called infiltrating or in situ.

Adenocarcinomas in situ

Adenocarcinoma in situ are confined to the ducts or lobules when discovered. Ductal carcinoma in situ (DCIS) accounts for eight to nine out of 10 in situ cancers. More rare, lobular cancer in situ (LCIS) accounts for 10 to 15% of in situ breast cancers.

Infiltrating adenocarcinomas

We speak of invasive cancer when the adenocarcinoma infiltrates the surrounding tissues. They develop from the cells of the ducts, we then speak of invasive ductal cancer: the tumor originates in the mammary ducts, crosses the wall and invades the neighboring breast tissue. Infiltrating lobular cancer begins in the lobules and then crosses the walls to invade the breast tissue.

Infiltrating cancers can affect the lymph nodes, particularly the axillary lymph nodes, located in the armpit. They can also affect other parts of the body and form metastases. This is called metastatic cancer.

There are other much rarer forms of carcinoma: medullary carcinoma, mucinous carcinoma (the cells secrete mucus), tubular carcinoma, papillary carcinoma.

Paget's disease of the nipple

Paget's disease of the nipple is a breast adenocarcinoma, a high-grade ductal cancer. “It begins in the milk ducts, which are the small tubes that carry milk to the nipple openings when a woman breastfeeds. It can then spread to the areola or deeper breast tissue,” notes the National Cancer Institute. A crust forms over the nipple and areola. They become red and the skin peels, leading to skin lesions.

Inflammatory breast cancer

Inflammatory breast cancer accounts for 1 to 4 percent of all breast cancer cases. Unlike the vast majority of breast cancers, which develop as a solid tumor, inflammatory breast cancer travels through the lymphatic vessels. “Cancer cells have the characteristic of moving rapidly in the lymphatic vessels of the skin of the breast, which they end up blocking. This is what causes local inflammation of the breast”,explains the National Cancer Institute. Symptoms are then visible: dimpled breast skin, tender breasts, lump or thickening of breast tissue, nipple discharge, change in appearance of the nipple, enlargement of the axillary lymph nodes. Sometimes confused with mastitis, diagnosis can be delayed.

Cancer subgroups

Hormone-dependent breast cancer:

This is a cancer that expresses receptors for hormones, estrogen and often progesterone. It represents 80% of all breast cancers and is the one with the best prognosis. Antihormonal treatment can be prescribed to block its progression.

HER2 overexpressed cancer

This cancer has a large number of receptors on the surface of its cells for the HER2 protein, a molecule that plays an essential role in the growth of the body and in tissue repair. In the case of breast cancer, it promotes the growth of cancer cells. It represents on average 12 to 20% of breast cancers. This is immunotherapy, which is a very effective treatment. Trastuzumab, a monoclonal antibody, blocks the HER2 protein and thus prevents the development of cancer.

Triple negative breast cancer

This group of cancers, 15% of patients, is characterized by the absence of receptors for hormones, estrogen and progesterone and HER2 receptors, which is why it is called triple negative and also why it is one of the most difficult cancers to treat. Indeed, treatments targeting these three markers are ineffective in this type of cancer. It is often found in young women who have a genetic predisposition.

Breast cancer in men

Breast cancer in men is rare and little known. This leads to delays in diagnosis. It is most often ductal carcinoma, which has positive hormone receptors. The genetic factor is the most frequent.

How is the stage of a cancer defined ?

The stage of the cancer – the extent of the disease at the time of diagnosis – is defined according to three criteria:

the size and infiltration of the tumor: carcinoma in situ concerns precancerous lesions and are discovered at a very early stage of the disease; whether or not the lymph nodes are affected: when they are affected, this means that the disease has started to spread. The number and location of the lymph nodes involved provide information on the level of progression of the disease; the presence or absence of metastases: the liver, bones and lungs are the three organs most frequently affected by breast cancer that has metastasized.

The stage results from the combined analyses of the trio "tumor, nodes and metastases", in English "tumor, nodes, metastasis". This TNM classification, from the International Union Against Cancer, is expressed in Roman numerals ranging from 0 to IV. For metastatic cancer, it is stage IV.

What does the grade mean ?

The grade of the cancer is used to define the aggressiveness of the tumor. It is the examination of the cell – anatomopathological examination – that will allow it to be defined. Its size, shape, architecture and the number of dividing cells (mitotic activity) are studied under a microscope. From the least aggressive to the most aggressive, tumors are classified from grade I (low grade) to grade 3 (high grade).