Epidemiology and Diagnosis
Breast cancer…
- is the most common cancer in US women aside from skin cancers
- accounts for about 30% of all new cancers in women each year
- mainly occurs in middle-aged and older women (median age at diagnosis is 62 years)
- is the second leading cause of cancer death in women (behind lung cancer). The chance that any woman will die from breast cancer is about 1 in 40 (~2.5%)1
2024 American Cancer Society estimates:
- ~310,720Â new cases of invasive breast cancer.Â
- ~56,500 new cases of ductal carcinoma in situ (DCIS). Â
- ~42,250Â deaths from breast cancer.
- The average risk of a woman in the US developing breast cancer sometime in her life is about 13%.1
However, there are reasons for optimism:
- Breast cancer death rates have been decreasing steadily since 1989.
- The declining death rate has been attributed to improved screening and awareness, along with improved treatments.
- At this time there are more than 4 million breast cancer survivors in the United States.1
Most common breast cancer symptoms:
The most common breast cancer symptoms include:
- Presence of a lump or thickening (a mass, swelling, skin irritation, etc) within or near the breast and in the underarm area as well
- Differences/changes in the shape or size of a breast
- Any changes in color or feel of the skin of the breast, areola, or nipple (eg, red, swollen, dimpled, puckered, etc)
- Changes in the nipple (eg, tenderness, discharge, inversion, erosion, color change)
Subtypes: Understanding HR and HER2:
HR stands for hormone receptor. HR+ means that tumor cells have receptors for the hormones estrogen or progesterone, which can promote the growth of HR+ tumors. HER2 stands for human epidermal growth factor receptor 2. HER2+ means that tumor cells make high levels of a protein called HER2/neu, which has been shown to be associated with certain aggressive types of breast cancer.2
Generally, breast cancer is divided into 5 major common clinical subtypes based on estrogen receptor (ER) expression, progesterone receptor (PR) expression, and HER2 expression or gene amplification.3 These 5 subtypes are the following:
(a) HR+/HER2− (ie, tumors expressing ER, PR, or both) that are HER2-negative
(b) HR+/HER2+ (ER+/PR−/HER2+, ER−/PR+/HER2+, and triple-positive [ER+/PR+/HER2+] disease)
(c) HR−/HER2+
(d) HR−/HER2− (or triple-negative: ER−/PR−/HER2−)
(e) HER2-low, defined as immunohistochemical detection of HER2 protein at a 1+ or 2+ level in tumor cells, and lacking amplification of the gene encoding HER2, encompassing both HR+ and HR− patientsÂ
Tumors classified as HR+/HER2− include those that are HER2-low and are the most common subtype, accounting for around 70% of all breast cancers.3 However, this rate appears to be increasing, with around 90% of new cases from 2017 to 2021 being HR+/HER2−.2Â
References
- American Cancer Society. Key statistics for breast cancer. https://www.cancer.org/cancer/types/breast-cancer/about/how-common-is-breast-cancer.html.
- National Institutes of Health (NIH). Cancer stat facts: female breast cancer subtypes.
https://seer.cancer.gov/statfacts/html/breast-subtypes.html. - Pegram M, Pietras R, Dang CT, et al. Evolving perspectives on the treatment of HR+/HER2+ metastatic breast cancer. Ther Adv Med Oncol. 2023;15:17588359231187201.
