Invasive (infiltrating) breast cancer
When breast cancers have spread from their place of origin (breast ducts or lobules) into the surrounding breast tissue they are classified as invasive or infiltrating cancers. This means they have the potential to invade into blood and lymph vessels and spread (metastasise) to other sites in the body.
Types of invasive breast cancer
Invasive carcinoma NST (also known as invasive ductal carcinoma)
This is the most common type of breast cancer, occurring in approximately 80% of cases and can occur in men as well as women. It is often described on a pathology report as NST (no special type) or NOS (not otherwise specified) as it doesn't have special distinguishing features when viewed under a microscope, unlike the rarer special types. It arises in the cells lining the breast ducts and invades through the duct wall into surrounding breast tissue. It's important to note that if you have been diagnosed with Ductal Carcinoma in Situ ( DCIS) this is not invasive ductal cancer.
Invasive lobular carcinoma (ILC)
Invasive lobular carcinoma is a cancer that has spread from the breast lobules into surrounding tissue. It is the second most common type of breast cancer, occurring in 8-10% of all cases. It may be multifocal (found in more than one place in the breast) and is sometimes found in both breasts.
ILC can sometimes be difficult to detect by physical examination or mammography as the cells tend to form in single file strands which don’t cause as much distortion of the breast tissue, and it may present as a thickening of the breast tissue rather than a hard mass.
Because it can sometimes be challenging to diagnose, lobular cancer is often larger when it’s found than other types of breast cancer. It tends to occur more often in women over the age of 45 and is rare in men. Classic lobular carcinoma tends to be Grade 2 and hormone receptor positive. There are rarer subtypes, such as pleomorphic lobular carcinoma, which tend to be higher grade and not hormone responsive. If you have been diagnosed with Lobular Carcinoma in Situ (LCIS) this is not lobular cancer.
Special types of invasive breast cancer
These are less common forms of invasive ductal breast cancer, and all have particular distinguishing features, which are seen under a microscope.
Paget’s Disease of the Breast
This rare type of breast cancer accounts for approximately 2% of all breast cancers and usually presents with a red, scaly or ulcerated nipple, sometimes accompanied by a burning sensation or discharge. The cancer cells accumulate in the ducts of the nipple but may extend out to the nipple surface. The skin changes sometimes extend to the areola but they first arise on the nipple. Paget’s Disease is often initially confused with eczema or other skin conditions. A full-thickness skin biopsy taken from the nipple/areola is usually required for diagnosis.Occasionally the disease is confined solely to the nipple, but the majority of people with Paget’s Disease will also have underlying DCIS or, in some cases, an invasive tumour in the breast.
Mucinous carcinoma (Colloid)
This is a rare form of invasive ductal cancer in which cancer cells are surrounded by mucin, a principal component of mucous. It accounts for 2-3% of all breast cancers, and tends to occur in women over 60. It is extremely rare in men. It is generally less aggressive and less likely to spread to the lymph nodes than other types.
This rare subtype of invasive ductal carcinoma has a tube-shaped structure when viewed under a microscope. Tubular cancer is usually low grade, slow growing and often small at diagnosis. It accounts for approximately 1% of breast cancers.
Medullary carcinoma accounts for about 3-5% of breast cancers. It is more common in BRCA1 mutation carriers and is more likely to affect women in their late 40s and early 50s. The tumours are often high grade and triple receptor negative, but despite these aggressive features, medullary cancer is less likely to involve the lymph nodes and tends to respond well to treatment. It was originally named because under a microscope the cells look similar to those in the medulla of the brain.
Papillary cancer is characterised by finger-like projections when viewed under a microscope. It can be DCIS or invasive cancer, or a mixture of both. This type of cancer is usually intermediate grade, less likely to involve lymph nodes and tends to affect older women.
This is an aggressive form of breast cancer with a high rate of lymph node involvement. The cells form in clusters with distinct clear spaces between them.
Cribriform (Adenoid cystic) carcinoma
Within these tumours there are distinctive holes between the cancer cells, giving it a Swiss cheese appearance. The tumour is usually low grade with a low rate of lymph node involvement.
This rare cancer accounts for less than 1% of breast cancers. It presents a mixed cellular picture and is characterised by metaplasia (change in form) where cancer cells transform from one type to another. It is commonly high grade and triple receptor negative.
Some breast cancers contain mixed tumour types. Ductal and lobular, for example, or tubulo-lobular.
Phyllodes means leaf-like, and these rare tumours grow in this pattern. Most Phyllodes tumours are benign, but approximately 10% are malignant (cancerous) and some are classed as borderline malignant. They mostly occur in women aged 40-50 and grow in the connective tissue of the breast rather than in the ducts. Phyllodes tumours are treated mainly with surgery. If breast conserving surgery is performed, rather than mastectomy, it is important to achieve widely clear margins, otherwise there is a strong potential for the tumour to recur.
There are some other rare tumours that don't originate in breast tissue but can also occur in the breast.
- Angiosarcoma. These are very rare tumours which arise in the cells lining the walls of blood and lymphatic vessels. Most cases occur in young women and the tumours grow quickly.
- Lymphoma of the breast. Primary lymphoma in the breast is very rare, and the majority of these cases are non-Hodgkins lymphomas. Breast lymphomas are more commonly secondary tumours arising from a primary lymphoma occurring elsewhere in the body. The treatment is for lymphoma rather than breast cancer.
- Breast implant-associated anaplastic large cell lymphoma. This is not actually a breast cancer but a rare form of non-Hodgkins lymphoma which can develop near textured breast implants. Most cases are cured by removing the implant and the surrounding capsule.
Inflammatory breast cancer
This is a rare and aggressive presentation of locally advanced, invasive carcinoma, occurring in less than 4% of breast cancer cases. Inflammatory breast cancer occurs more commonly at a younger age than other breast cancers. A high BMI (body mass index) is thought to increase the risk of developing inflammatory breast cancer.
It presents as progressive inflammation of at least one third of the breast. The onset is usually rapid over several weeks.
The breast skin becomes warm and feels thick, and may have an orange peel appearance (peau d’orange). This is caused by cancer cells spreading through and blocking lymphatic vessels under the skin. The skin may be flushed pink initially and progress to appear red or purple. The breast becomes swollen and enlarged and may feel heavy. Enlarged lymph nodes can often be felt in the axilla, but in many cases a distinct breast lump can’t be felt. In some cases the nipple may become flattened or inverted.
Inflammatory breast cancer is often confused with a breast infection (mastitis), but shows no improvement when treated with antibiotics.
In most cases there is lymph node involvement, and because of the high risk of distant metastases, CT and bone scans are performed to stage the disease and aid treatment planning. Neo-adjuvant chemotherapy (given before surgery) is required to shrink the tumour to enable surgical removal. Mastectomy and axillary node dissection is usually required, followed by radiation therapy. Herceptin and hormonal therapy are given when appropriate.