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Breast cancer: What type is it?

Dr Khoo Kei Siong from Parkway Cancer Centre looks at the different types of breast cancer that a woman may get.

Last year, more than two million cases of breast cancer were diagnosed around the world, making it the most common cancer in women worldwide, according to the World Cancer Research Fund. In Singapore, too, breast cancer is the most common cancer among women.

All women are at risk of getting breast cancer, of which there are several types. These are differentiated in different ways – depending on how the cancer cells look under the microscope (called histology); on whether the cancer cells have certain characteristics (receptor status); and on whether they are localised or have spread (stage).

In diagnosing breast cancer, doctors have to distinguish these types of breast cancer carefully so that they can recommend the most appropriate treatment plan for their patients.

Based on histology

Common types

Invasive ductal carcinoma (IDC): This is the most common type of breast cancer and accounts for 70 to 80 per cent of all cases of invasive breast cancer. The cancer grows in the cells lining the milk ducts in the breast, which then break through the duct wall and invade the breast tissue around the area. These cells may also spread to other organs and parts of the body.

Ductal carcinoma in situ (DCIS): This is the non-invasive form of IDC, when the cancer does not spread to the surrounding breast tissue. It is also the most common type of non-invasive breast cancer. As it is non-invasive, DCIS is highly treatable, often with surgery alone. It should not be left untreated, however, as it can turn into invasive cancer and spread to other parts of the body.

Invasive lobular carcinoma (ILC): About 10 per cent of breast cancers diagnosed are of this form of breast cancer, which tends to affect women between 45 and 55 years old. The cancer starts in the cells in the lining of the lobules, the glands that produce milk, and may spread to other parts of the body.

Lobular carcinoma in situ (LCIS): This non-invasive form of ILC is also known as lobular neoplasia. As LCIS shows no symptoms and cannot be seen with a mammogram, it is usually diagnosed during tests or spotted while treatment is being given for other breast conditions.

Less common types

Medullary carcinoma: Seen in less than 1 per cent of all breast cancer cases, medullary breast cancer tends to hit women who have the inherent faulty BRCA1 gene. The cancer cells are bigger and there is usually a clear demarcation between the tumour and normal tissue.

Tubular carcinoma: Under the microscope, the cancer cells of this form of breast cancer look like tubes. Seen in about 2 per cent of all breast cancer cases, tubular carcinoma tends to affect older women in their 50s and above. It is usually diagnosed through a mammogram.

Inflammatory breast cancer: This aggressive and fast-growing form of breast cancer is seen in 1 to 5 per cent of all breast cancer patients. It can invade the skin and block lymph channels, which can cause redness, swelling and thickening of the overlying skin, and diffuse firmness of the breast. 

Mucinous (colloid) carcinoma: Affecting 1 to 3 per cent of breast cancers, this slower-growing cancer tends to affect older women.

Paget disease of the nipple: This cancer, which accounts for 1 to 4 per cent of breast cancers, starts in the breast ducts and spreads to the nipple and the areola – the darker area of the skin around the nipple. It can irritate both and cause them to be scaly, itchy and red.

Receptor types

Breast cancers also have different biological characteristics, depending on the presence or absence of receptors such as estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). These characteristics also affect how the cancer behaves and how it needs to be treated – in some cases, even more than the histology of the cancer.

Hormone receptor-positive breast cancer: Most types of breast cancer (up to 70 per cent) are positive for ER or PR, or both. Such cancers tend to be slower-growing and less aggressive, and patients are, therefore, more likely to have a better long-term outcome. These cancers are usually treated with hormonal therapy such as tamoxifen and aromatase inhibitors. 

HER2-positive breast cancer: Some 15 to 25 per cent of women are affected by HER2-positive cancer. This cancer arises when there are excess quantities of the human epidermal growth factor (HER2) protein – found on the surface of normal breast cells – thus causing cells to grow and divide abnormally.

Triple negative breast cancer: This form of cancer does not have ER, PR, or HER2 receptors, and is usually aggressive. The rate of relapse is high, and survival rates are poor. Triple negative breast cancer accounts for about 15 per cent of breast cancers, and tend to affect women under 40 and those with a faulty BRCA1 gene. 

Stages

Early breast cancer: A large majority (about 90 per cent) of breast cancers are found when they are still localised in the breast and in the lymph nodes in the axilla (armpit) on the same side. These Stage 1, 2 or 3 cancers are potentially curable and are usually treated with surgery, chemotherapy, hormonal therapy or radiotherapy (or combinations). 

Metastatic breast cancer: Metastatic or Stage 4 breast cancer occurs when a cancer spreads from the breast to other organs and parts of the body. It is sometimes also called secondary or advanced breast cancer. While such cancers may be detected when the disease is first diagnosed, they are more commonly caused by a recurrence of an earlier round of breast cancer. While they are not usually curable, they can be treated to prolong survival and improve quality of life.

Screening: When & What

39 years & below

• Monthly breast self-examination

40–49 years

• Monthly breast self-examination
• Annual screening mammography

50 years & above

• Monthly breast self-examination
• Two-yearly screening mammography