How is breast cancer diagnosed ?
A biopsy, the only way to diagnose breast cancer
Half of breast cancers are diagnosed between the ages of 50 and 69, 20% before the age of 50, and 10% before the age of 40 (source: ARCAGY). Performing medical imaging tests alone is not sufficient to establish the precise diagnosis of breast cancer.
PTo perform this, it will be necessary to perform a biopsy to access the suspicious tissue and its cells to determine their benign or tumoral nature. This examination will be carried out by a radiologist who, under local anesthesia, will take a tissue sample using a needle.
If a larger biopsy is necessary, it will then be performed by a surgeon, most often under general anesthesia. This tissue sampling will be done in the area that appeared suspicious during mammography, ultrasound, or clinical examination.
This sample will be treated with various dyes and reagents in a histopathology laboratory. It will then be examined under a microscope by a pathologist, a specialist in the analysis of organs, tissues, and cells. It will take about a week to ten days before the results seen under the microscope are reported by the doctor.
The pathologist will first determine the nature of the observed cells. They may correspond to a non-invasive cancer, meaning a cancer that is confined to the immediate area where it began and has not invaded adjacent tissues or other organs. These non-invasive cancers represent 15 to 20% of breast cancers.
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Non-invasive breast cancers , also called " carcinomas in situ ," are cancers that are in an early stage. There are two different types: ductal carcinomas in situ (80 to 90% of non-invasive cancers) and lobular carcinomas in situ (10 to 15% of non-invasive cancers).
The former are almost always discovered in women after menopause and during a mammogram. On images, the radiologist observes microcalcifications in nearly 70% of cases. These ductal carcinomas in situ remain confined to the lactiferous ducts , the ducts that carry milk from the glands that produce it to the nipple. The prognosis for these cancers is excellent, but they need to be treated because untreated, they tend to progress to an invasive form.
Lobular carcinomas in situ are often discovered incidentally in women before menopause and during a biopsy. These carcinomas remain confined to the lobules whose cells produce milk. 70% of patients with lobular carcinoma in situ will not develop invasive cancer . Patients with this type of cancer will benefit from regular monitoring and biopsy if there is any doubt.
Examining the tissue sample, the pathologist can also make a diagnosis of invasive cancer (invasive carcinoma). These cancers tend to invade surrounding tissues and can metastasize.
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As with non-invasive cancers, there are two main types of invasive cancers depending on their origin:
- Ductal carcinomas , which begin in the milk ducts and extend beyond these ducts. They represent 80% of invasive cancers.
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Lobular carcinomas
, which begin in the lobules and extend beyond these lobules. They represent 10% of invasive cancers.
There are rarer forms of invasive breast cancers such as medullary cancers or mucinous cancers .
The examination of the tissue sample will also determine the grade of the cancer cells, which is the appearance of cancer cells compared to normal cells. The grade will help specify the therapeutic strategy and evaluate the prognosis of the disease.
Learn more about determining cancer grade
Classified from 1 to 3, the higher the grade, the more the appearance of cancer cells deviates from that of a normal cell and the more aggressive the cancer cells are.
Grade 1 cancers (well-differentiated cancers) have cells with a relatively normal appearance and low multiplication.
Grade 3 cancers (poorly differentiated cancers) have highly undifferentiated cells and high multiplication.
Grade 2 cancers (moderately differentiated cancers) have characteristics intermediate between stage 1 and stage 3 cancers.
On the tissue sample, the pathologist will study the level of expression of the Ki67 molecule, which is an excellent marker of cell proliferation. The higher the Ki67, the more tumor cells proliferate.
They will also study the presence or absence of three important molecules that, when present on the surface of tumor cells, promote their multiplication: estrogen receptors (ER), progesterone receptors (PR), and human epidermal growth factor receptor 2 or HER2. The results of this study are very important as they will determine the treatment of the cancer.
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Precise histopathological analysis combined possibly with molecular profiling.
There are different types of breast cancer, the treatments of which differ depending on the presence of hormonal receptors, HER2, or other mutations or molecular profiles. It is very important to be able to have a precise analysis of the tumor complemented, in some cases, by additional deeper molecular and biological analyses to optimally adapt the treatment to each particular case.
For some more aggressive cancers resistant to treatments, this also allows access to clinical trials with new targeted molecules and innovative treatments.
Breast cancer subtypes
For the management of breast cancers, 5 subtypes of cancers are distinguished, which will be treated differently depending on the expression of the hormonal receptors ER and PR, HER2, and the proliferation marker Ki67:
- ER+ low-risk breast cancers (Luminal A): strongly express estrogen receptors and progesterone receptors. They do not express HER2. The Ki67 proliferation marker is low. They represent approximately 45% of breast cancer cases and have the best prognosis.
- ER+ high-risk breast cancers (Luminal B): express estrogen receptors less strongly. They may or may not express progesterone receptors. They do not express HER2. The Ki67 proliferation marker is high. They represent approximately 25% of breast cancer cases.
- HER2+ ER- breast cancers: express HER2 but do not express estrogen receptors or progesterone receptors. They represent 5% of breast cancer cases.
- HER2+ ER+ breast cancers: express HER2 and estrogen receptors. They may or may not express progesterone receptors. The Ki67 proliferation marker is high. They represent 10% of breast cancer cases.
- Triple-negative breast cancers: do not express any of the three receptors ER, PR, and HER2. They represent 10 to 15% of breast cancer cases and are the most aggressive breast cancers.
(source : Cell, 2023)
The pathologist can also study the expression of the PD-L1 checkpoint on the surface of tumor cells.
💡 DID YOU KNOW ?
The PD-L1 checkpoint is utilized by cancer cells to inhibit the functioning of the immune system.
A strong expression of PD-L1 favors a good response to immunotherapy directed against PD-L1. This immunotherapy will prevent PD-L1 from inhibiting the functioning of the immune system.
Molecular analyses and staging assessment
Furthermore, the diagnosis of breast cancer may require additional analyses to be conducted in a molecular biology laboratory. In such a laboratory, mutations that may occur in genes are studied. In the case of breast cancer, mutations that will be particularly studied are those affecting the BRCA1 and BRCA2 genes.
Other genes such as PIK3CA, GAT3, MAP3K1, or CDH1 are frequently mutated and may also be studied to select a potential treatment targeting one of these genes.
Once the diagnosis of breast cancer is established, a staging evaluation is performed. This evaluation includes medical imaging examinations such as an abdominal-pelvic ultrasound, a chest X-ray, a bone scan, a thoraco-abdominal CT scan, and Positron Emission Tomography (PET) scan.
Biological tests will also be conducted, including the measurement of a biological marker, CA 15-3. This staging evaluation will establish the stage of the cancer.
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Determining the stage of cancer is primarily of therapeutic interest, as knowledge of this stage will help establish the most appropriate treatment for the patient. It will also predict the most likely course of the disease.
The stage of cancer is determined based on three criteria. The first criterion depends on the characteristics of the tumor (T); The second criterion depends on the number of involved lymph nodes [N for Node]; the third criterion depends on the presence of metastases and the number of organs affected by them (M). These three criteria help define the stage of cancer and classify cancers according to an internationally recognized classification (TNM classification).
A Stage 1 breast cancer corresponds to a tumor of 2 cm or less in diameter that does not appear to have spread beyond the limits of the breast. No lymph nodes are affected, and there are no distant metastases.
A Stage 2 breast cancer corresponds to a tumor larger than 2 cm in diameter and less than 5 cm and/or has spread to lymph nodes in the armpit on the same side of the breast cancer.
A Stage 3 breast cancer corresponds to a tumor larger than 5 cm in diameter that has spread to lymph nodes located behind the sternum. There are no signs of extension to distant organs or to lymph nodes distant from the breast, such as those under the clavicle.
A Stage 4 breast cancer corresponds to a tumor that has metastasized to distant organs such as bones, lungs, or lymph nodes distant from the breast.
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Article updated on Sep 27, 2024
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