Atypical breast hyperplasia and cancer risk
- Lesion
Atypical hyperplasia looks like a tiny low-grade cancer that has not filled its space; it signals a clearly higher risk of breast cancer in both breasts.
What it is
Atypical hyperplasias are clonal proliferations that share features with low-grade carcinoma in situ but are too limited in extent to be called so. Atypical ductal hyperplasia resembles low-grade DCIS in only part of a duct; atypical lobular hyperplasia resembles lobular carcinoma in situ but fills less of the lobule; flat epithelial atypia is a layer of mildly atypical columnar cells. They share molecular changes with low-grade, estrogen-receptor positive cancers and raise the risk of breast cancer about four to five times, in either breast.
Structure
- Atypia is defined by monotony: cells all alike, with round nuclei and crisp borders, unlike the varied cells of usual hyperplasia.
- Lobular atypia: cells lose cohesion because E-cadherin is gone; intracytoplasmic mucin vacuoles may be seen.
- All atypical lesions keep an intact myoepithelial layer and basement membrane.
Step by step
- A clone of luminal cells acquires early changes shared with low-grade cancers, such as loss of 16q and gain of 1q.
- The clone grows as a uniform population (atypical hyperplasia) that does not yet fill the duct or lobule.
- In some patients the clone enlarges into low-grade DCIS or LCIS and later invades.
- The same field of altered breast tissue increases risk elsewhere in both breasts.
Benign breast lesions and the later risk of invasive cancer
| Category | Examples | Relative risk of breast cancer |
|---|---|---|
| Nonproliferative | Cysts, apocrine metaplasia, fibrosis, adenosis, simple fibroadenoma | No increase |
| Proliferative without atypia | Usual ductal hyperplasia, sclerosing adenosis, radial scar, papilloma, complex fibroadenoma | Slightly increased (about 1.5 to 2 times) |
| Proliferative with atypia | Atypical ductal or lobular hyperplasia | Moderately increased (about 4 to 5 times) |
| Carcinoma in situ | Lobular carcinoma in situ; DCIS (ipsilateral) | High (about 8 to 10 times) |
Markers
- E-cadherin (lost in lobular lesions)
- ER strongly positive
- CK5/6 negative (monoclonal luminal cells)
Clinical notes
- Atypia on a core biopsy usually leads to surgical excision because carcinoma may be found next to it.
- Women with atypical hyperplasia are offered closer surveillance and may be offered endocrine risk-reducing therapy.
Test yourself
Think of the answer, then tap the question to see it.
How does atypical ductal hyperplasia differ from low-grade DCIS?
It has similar monomorphic cells but only partly fills ducts or is very limited in extent.
How much does atypical hyperplasia raise breast cancer risk?
About four to five times, and in both breasts.
Which protein is lost in atypical lobular hyperplasia?
E-cadherin, which explains the discohesive cells.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Fibrocystic Breast Disease (StatPearls (NCBI Bookshelf), 2026); Genetics of Breast and Gynecologic Cancers (PDQ®)–Health Professional Version (National Cancer Institute, 2026).
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Representative model, for educational purposes only.