Breast cancer is the most common malignancy among women. It is the second leading cause of death due to cancer in women worldwide. Statistics of breast cancer have revealed an estimate of 231,840 new cases of invasive breast cancer and 60,290 additional cases of in situ breast cancer will be diagnosed among women in 2017 (American Cancer Society, 2017). Risk of breast cancer increases with the age, women above the age of 40 is more prone to the risk breast cancer. About 5-10% of breast cancer cases are thought to be caused by inherited changes to certain genes such as BRCA1 and BRCA2. Furthermore, women already exposed to radiation have a higher risk of developing breast cancer over the course of lifetime. Other factors such as unhealthy diet, overconsumption of alcohol, being overweight, combination hormone therapy (with estrogen and progesterone) may likely increase the risk of breast cancer in women. Various lines of treatment including surgery (both curative and preventive), radiation therapy, systemic chemotherapy, endocrine therapy and targeted therapy that interfere with the cellular functions thereby inducing cell cycle arrest and eventually apoptosis, a form of programmed cell death,. However, treatment of breast cancer depends largely on the tumor stage, histological grades and its expressed biomarkers. Some established biomarkers such as ER (Estrogen Receptor) and PR (Progesterone Receptor) have been identified as strongest predictive factors, whereas human epidermal growth factor receptor 2 (Her2 or c-erbB2) receptors found to be predictive as well as prognostic factors for breast cancer therapy (Florea, Busselburg et al. 2013). Despite tremendous advances, breast cancer treatment still remains a challenge due to development of resistance to various therapies.
1.1 Breast Cancer Classification
The classification of breast cancer has been done on the basis of histology and molecular biomarkers.
1.1.1 Histological classification of breast cancer subtypes: Based on the histopathological classification the three most common types of breast cancer are:
· Ductal Carcinoma in situ (DCIS)
· Invasive Ductal Carcinoma (IDC)
· Invasive Lobular Carcinoma (ILC)
184.108.40.206 Ductal Carcinoma in situ (DCIS)
DCIS is known as non-invasive carcinoma and is contained inside the ducts. It signifies the early form of breast cancer. In some cases, DCIS may become an invasive cancer and spread out of the ducts into nearby tissue and could metastasize to other parts of the body. It is the most common type of pre-cancer in women. DCIS has been further classified into five subtypes: Comedo, Cribiform, Micropapillary, Papillary and Solid depending on tumor architecture (Ajisaka, Tsugawa et al. 2002). This scheme of classification is currently used by clinicians for disease prognosis.
220.127.116.11 Invasive Ductal Carcinoma (IDC)
Invasive ductal carcinoma is the most common type of breast cancer. IDC starts with in the cells of milk ducts and spread into the nearby breast tissues and other parts of the body via lymph channel and blood stream.
18.104.22.168 Invasive Lobular Carcinoma (ILC)
Invasive Lobular Carcinoma begins in the lobules (milk producing gland) and it can metastasize to other parts of the body. ILC is less common type of breast cancer then IDC. Due to their distinctive growth pattern and biology, ILC may be harder to diagnose at early stages then IDC (Singletary, Parekh et al. 2005).
There is some other less common type of invasive breast cancer:
22.214.171.124 Inflammatory breast cancer (IBC): Inflammatory breast cancer is rare and different from other types of breast cancer. IBC is more aggressive type of breast cancer as it grows and spread much faster than the other types of breast cancer. Symptoms of IBC include swelling and redness of the skin of the breast. IBC cause the blockage of lymph vessels in the skin of the breast (Gonzalez-Angulo, Hennessy, et al. 2007).
126.96.36.199 Paget disease of the nipple: In Paget disease of the nipple, cancer cells collect in or around the nipple. Paget disease of the nipple cause scaly, crusted and red skin of the nipple. Other uncommon, special subtypes of breast cancer are medullary mucinous, papillary and tubular carcinoma (Karakas, 2011).