Invasive Breast Cancer
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Breast cancer occurs in two broad categories: noninvasive and invasive. Noninvasive breast cancers stay within the milk ducts or lobules, and do not grow into normal tissues inside or outside the breast. Noninvasive cancers are sometimes referred to as carcinoma in situ or pre-cancers.
By contrast, invasive breast cancers are those that have spread to the normal tissues within or surrounding the breast. Invasive breast cancer may also spread to other parts of the body through the blood and lymph systems. Invasive breast cancer, also called infiltrating breast cancer, is the most common type of breast cancer among American women. According to the American Cancer Society, 207,090 new cases of invasive breast cancer were diagnosed in women in 2010.
Sometimes, breast cancer can be both invasive and noninvasive: some of the cancer cells have grown into normal tissue and some has remained in the ducts or lobules. This type of cancer is treated as an invasive cancer. In some invasive breast cancers, malignant cells may be present in both the ducts and lobues. This type of “mixed tumor” breast cancer is usually treated as ductal carcinoma.
There are two main types of invasive breast cancer: invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC). IDC begins in the milk ducts and accounts for 70% or more of invasive breast cancers. ILC begins in the lobules and is more rare. Sometimes, the origin of the tumor may not be known.
Invasive Breast Cancer Subtypes
There are also several subtypes of invasive breast cancer, including:
- Endocrine-sensitive breast cancer: Breast cancer cells contain measurable amounts of estrogen or progesterone receptors, making the cancer treatable with hormonal therapies
- HER2-positive breast cancer: Breast cancer cells contain excess amounts of the HER2 receptor, making the cancer treatable with anti-HER2 targeted therapies
- Triple-negative breast cancer: Breast cancer cells do not contain receptors for estrogen, progesterone, or HER2. This type of cancer cannot be treated with hormonal or anti-HER2 therapy, but can be treated with chemotherapy, radiation, and non-HER2 targeted therapy.
- Inflammatory breast cancer: Invasive cancer in which there is no lump or tumor.
Medullary carcinoma: A less common type of IDC where the tumor is soft and fleshy (resembling the medulla in the brain).
- Metaplastic carcinoma: A rare type of invasive breast cancer where a portion of the tumor cells have changed to a different type of breast cancer (a mixed tumor)
- Mucinous carcinoma: A less common type of IDC, the tumors create thick pools of mucin, a main component of saliva.
- Papillary carcinoma: A rare type of IDC that forms in distinct lumps with finger-like projections.
- Tubular carcinoma: A less common type of IDC made of collections of small, tube-like cells less than 1 cm in diameter.
- Paget’s disease: Any of the above forms of breast cancer that directly involves the nipple.
Male breast cancer: A rare form of breast cancer, accounting for less than 1% of all breast cancers. Breast cancer in men usually begins as a lump or mass in a man’s breast, and is most commonly treated with a mastectomy or lumpectomy.
Invasive Breast Cancer Risk Factors
Most breast cancers are invasive. Anyone may be diagnosed with invasive breast cancer. Factors that may increase risk include:
- Gender: Women are at greater risk than men for developing invasive breast cancer.
- Race: Invasive breast cancer rates are lower among black, Asian and Hispanic women and higher among white women.
- Age: Women who are age 55 years and older are at greater risk for invasive breast cancer than women under age 55.
- BRCA1 and BRCA2 Mutations: BRCA1 and BRCA2 are genes that help repair damaged DNA. Mutations in BRCA1 and BRCA2 can be inherited from a family member and are the most common causes of inherited breast cancer, which is most often invasive.
- Other genetic mutations: Other genetic mutations that may increase a woman’s risk of invasive breast cancer include ATM, p53, CHEK2, PTEN and CDH1. These mutations are rare and do not increase risk as much as BRCA1 and BRCA2.
- Family history of breast cancer: Having a family history of breast cancer, particularly women with a mother, sister or daughter who has or had breast cancer, may double the risk.
- Dense breast tissue: Women with less fatty tissue and more glandular tissue in the breast may be at higher risk for developing invasive breast cancer.
- Not having children: Women who have had no children, or who were pregnant later in life (over age 35) may have a greater chance of developing breast cancer. Breast-feeding may help to lower the risk of breast cancer.
- Obesity: After menopause, fat tissue may contribute to increases in estrogen levels, and high levels of estrogen may increase the risk of breast cancer. Weight gain during adulthood and excess body fat around the waist may also play a role.
Invasive Breast Cancer Symptoms
Screening mammograms may help detect breast cancer before it causes any symptoms. However, screening mammograms may miss breast cancer that is already present. Invasive breast cancer symptoms may include:
- A lump or mass in the breast
- Swelling of all or part of the breast, even if no lump is felt
- Skin irritation or dimpling
- Breast or nipple pain
- Nipple retraction (turning inward)
- The nipple or breast skin appears red, scaly, or thickened
- Nipple discharge
- A lump or swelling in the underarm lymph nodes
Knowing the signs and symptoms of breast cancer is essential to early diagnosis. For additional breast cancer information, please explore our Breast Cancer section and talk to your healthcare provider.