Triple-negative breast cancer (TNBC) is a distinct type of breast cancer. The term “triple-negative” indicates that the cancer cells lack three specific features commonly found in other breast cancers: receptors for the hormones estrogen (ER) and progesterone (PR), and an excess of the HER2 protein. These receptors normally help fuel cancer growth in other breast cancer types, allowing for targeted hormone therapies or HER2-blocking drugs. Since TNBC cells do not have these receptors, those specific treatments are not effective, making it a unique challenge in cancer care.
Visible Signs and Symptoms of TNBC
Changes in one’s body are often the first step in identifying a potential breast concern. A noticeable lump or mass in the breast is a common sign. It may feel firm and have irregular edges, differing from more movable, benign lumps.
The skin covering the breast might also show alterations, such as dimpling that resembles an orange peel, a condition known as “peau d’orange”. Redness, thickening, or scaling of the skin are other possible visual indicators. Changes in the breast’s overall size or shape, where one breast appears different from the other, can also occur.
The nipple itself might exhibit changes, including turning inward, a phenomenon called nipple retraction. Some individuals may also notice discharge from the nipple that is not breast milk. While these symptoms can be associated with TNBC, they are not exclusive to this type of cancer and can arise from other conditions; therefore, any observed changes warrant a medical evaluation.
Diagnostic Imaging of TNBC
Doctors use imaging techniques to identify suspicious areas inside the breast. Mammography, a specialized X-ray, is often one of the first diagnostic tools. On a mammogram, TNBC tumors commonly appear as high-density masses, often with a round or oval shape. Irregular or indistinct margins can also be observed.
Following a mammogram, an ultrasound may be used to further examine abnormal areas. This imaging uses sound waves to create detailed pictures, helping determine if a lump is solid or fluid-filled. TNBC masses on ultrasound frequently appear as hypoechoic (darker) masses, often with a round or oval shape. Posterior acoustic enhancement, where the area behind the mass appears brighter, can also be a feature.
Magnetic Resonance Imaging (MRI) offers another detailed view, useful for assessing tumor size and extent, especially in dense breast tissue. TNBC appears on an MRI as a discrete enhancing mass. A common feature is rim enhancement, where the outer edges of the mass light up brightly after a contrast agent is injected, suggesting active blood vessel growth within the tumor. These masses can also appear round, oval, or lobular, and may show high signal intensity on T2-weighted images, sometimes indicating tumor necrosis.
Microscopic Appearance of TNBC Cells
A definitive diagnosis of TNBC relies on examining tissue samples under a microscope after a biopsy. Pathologists analyze these samples to confirm cancer and identify specific characteristics. Immunohistochemistry (IHC) staining is performed to determine if a breast cancer is triple-negative.
During IHC, specific antibodies are applied to thin slices of tissue. These antibodies bind to estrogen receptors (ER), progesterone receptors (PR), and the HER2 protein if present on cancer cells. A chemical reaction produces a color change, making these receptors visible. For TNBC, cells do not show this color change when tested for ER, PR, and HER2, meaning they are “negative” for all three. This lack of staining confirms the diagnosis. The cells often have distinctive pathological features, including a higher histological grade, indicating faster growth, and may show central necrosis or fibrosis.
Staging and Imaging Metastasis
After a TNBC diagnosis, doctors determine the cancer’s stage, which describes how much cancer is present and if it has spread. This process guides treatment decisions and predicts outcomes. Imaging tests detect if the cancer has spread beyond the breast to other parts of the body, a process called metastasis.
Positron Emission Tomography (PET) scans, often combined with Computed Tomography (CT) scans (PET/CT), are commonly used. A PET scan involves injecting a small amount of a radioactive sugar tracer, usually 18F-FDG, into the bloodstream. Cancer cells are more metabolically active and consume more sugar than normal cells, causing them to light up brightly on the PET scan. This allows doctors to identify areas of potential cancer spread, such as in lymph nodes or distant organs like the lungs, liver, or bones. For aggressive subtypes like TNBC, PET/CT is helpful for systemic staging, even in earlier clinical stages, to detect unsuspected spread.