Breast Cancer Diagnosis and Classification

Breast cancer is the second most occurring cancer for women in the United States. It is estimated that there are 230,000 new cases arising in American women annually. It also occurs in men, but at a much lower rate of 2,300 annually.

Breast cancer is a form of carcinoma, cancer that originates from epithelial cells. The type of breast cancer is determined through a series of tests on breast tissue by a pathologist, a physician specialized in examining tissues in order to diagnose disease and recommend treatment. The pathologist examines the tissue through a microscope and identifies if cancer is indeed present and whether it is “in situ”, meaning non-invasive, or if it is invasive. Non-invasive cancers stay within their origin tissue, and have not yet spread to other normal tissue but invasive cancers have spread out to once noncancerous cells. For invasive cancers, the cancer is graded 1 to 3, through a comparison of the patient’s breast tissue with normal healthy tissue. The lower the grade, the less likely the patient has a cancer that will spread further. The higher the grade, the faster growing the cancer is, and therefore the larger the probability of spreading.  

Additionally, breast cancer cells can have estrogen receptors (ER+), progesterone receptors (PR+), both receptors or neither receptors. Two-thirds of breast cancer types have at least one of these hormone receptor types. The receptors allow cancer cells to obtain and utilize their respective hormones to fuel their development. Furthermore, one in five of breast cancers have too much HER2/neu, a protein that fosters cell growth. HER2/neu positive cancers are more invasive than other types. The amount of HE2/neu is usually identified through immunohistochemistry, an antibody test that changes cell color in response to an overabundance of HE2/neu, or a fluorescent in situ hybridization test (FISH) that uses fluorescent pieces of DNA to bind to the HER2/neu gene in cancer cells.  A triple negative cancer doesn’t have estrogen or progesterone hormone receptors and doesn’t have too much HER2/neu. Conversely, a triple-positive cancer is ER+, PR+ and HER2+.

A PAM50 test, working through identification of patterns of molecular features, is another classification method and divides breast cancer into 4 types. These are Luminal A, Luminal B, HER2 type and basal type. Luminal A/B cancers are ER+ cancers, but A type cancers are low grade, slow growth. B type cancers are high grade, fast growth.  HER2 type cancers are high grade and result from excessive copies of the HER2 gene in cells. Basal type cancers are triple negative type cancers, high grade, and require different treatment than the other types.

The extent the cancer has spread through the body can further be identified through more tests such as a chest x-ray, CT scan, bone scan, MRI, ultrasound and or PET scan. These tests allow the determination of the “stage” of the cancer in the body and are not usually used for early stage cancers. The most common system for “staging” used is the American Joint Committee on Cancer (AJCC) TNM system. T stands for primary tumor and is ranked zero to four, indicating the tumor size and spread to chest or skin. N stands for nearby lymph nodes and is ranked zero to 3, indicating if nearby lymph nodes have cancer and how many are cancerous. M stands for metastasis and is ranked 0 or 1, with 1 indicating the cancer has reached distant organs from the source. Combinations of the TNM ratings determine the stage of the cancer, from Stage I to Stage IV, with non-invasive cancers at Stage 0. Larger numbers for the TNM system indicate greater size, spread and severity.

Continuing research into cancer will augment our understanding of the mechanics of breast cancer and how to treat it. The fast pace of advancement in the medical field means that some of the current methods for diagnosing breast cancer may even become obsolete or new technologies may be invented. As such, the way breast cancer is diagnosed and classified is “subject to change”.

Written By: Kevin Yiu




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