Atypical lobular hyperplasia (ALH) is a benign breast condition where abnormal cells grow inside the milk-producing glands (lobules) of the breast. It is not cancer, but it roughly triples the risk of developing breast cancer later in life. ALH is found in about 10% of breast biopsies and is most commonly diagnosed in women in their 40s.
What ALH Looks Like Under a Microscope
In normal breast tissue, cells inside the lobules stick tightly together and form organized structures. In ALH, the cells lose that stickiness. Pathologists describe them as “discohesive,” meaning they don’t bind to each other the way healthy cells do. This happens because of a loss of a protein called E-cadherin, which normally acts like glue between cells. The cells themselves look relatively uniform and have minimal abnormality, but their looseness and growth pattern are what flag them as atypical.
ALH is closely related to a condition called lobular carcinoma in situ (LCIS). The cells look identical under a microscope. The distinction comes down to quantity: if less than 50% of the ducts within a lobular unit are filled with these abnormal cells, it’s classified as ALH. If 50% or more are involved, it’s upgraded to LCIS. Both are considered markers of increased breast cancer risk rather than precancerous lesions that will inevitably progress.
How ALH Affects Breast Cancer Risk
A large retrospective study published in The Lancet followed 252 women diagnosed with ALH by biopsy alone. Of those women, 50 (about 20%) went on to develop invasive breast cancer. The overall relative risk was 3.1, meaning women with ALH are roughly three times more likely to develop breast cancer compared to the general population. Some surgical sources cite the risk as four to five times higher, depending on the study and follow-up period.
One important detail: this increased risk applies to both breasts, not just the one where ALH was found. The ipsilateral breast (the same side as the biopsy) carries a slightly higher risk, but the contralateral breast is also at elevated risk. This is why ALH is considered a general risk marker for breast cancer rather than a localized precursor that will turn into cancer at the exact spot where it was found.
What Happens After a Diagnosis on Core Biopsy
ALH is often discovered incidentally when a core needle biopsy is performed to investigate an imaging finding like a suspicious area on a mammogram. When this happens, the question is whether you need a follow-up surgical excision to make sure nothing more concerning is hiding in the surrounding tissue.
The answer has shifted over the past decade. Guidelines from the American Society of Breast Surgeons now say that observation (without surgery) is reasonable for ALH diagnosed on core biopsy, as long as certain criteria are met: the imaging and pathology results are consistent with each other, the amount of abnormal tissue is small, there are no other high-risk features, and you continue with regular follow-up imaging. Current NCCN guidelines similarly recommend a case-by-case approach, with shared decision-making between you and your care team that factors in your personal and family history.
This doesn’t mean surgery is off the table. If the imaging doesn’t match the biopsy findings, if there are additional concerning features, or if there’s a strong family history of breast cancer, excision may still be recommended to rule out something that the core needle missed.
Screening and Ongoing Monitoring
After an ALH diagnosis, enhanced screening becomes part of your routine. The specifics depend on your overall lifetime risk of breast cancer, which your doctor can calculate using models that factor in your age, family history, and biopsy results.
The American Cancer Society recommends that women with a lifetime breast cancer risk of 20% to 25% or greater get both a mammogram and a breast MRI every year, typically starting at age 30. ALH on its own may or may not push your calculated lifetime risk above that 20% threshold, but when combined with other factors like family history or genetic mutations, it often does. For women whose lifetime risk falls below 15%, MRI screening is generally not recommended. The gray zone between 15% and 20% is where individual circumstances guide the decision.
How ALH Differs From Other Atypical Findings
ALH is sometimes confused with atypical ductal hyperplasia (ADH), but the two are distinct conditions. ADH involves the breast ducts rather than the lobules, and the cells behave differently. ADH cells are cohesive (they stick together), form rigid architectural patterns, and test positive for E-cadherin. ALH cells are the opposite: loose, lacking E-cadherin, with a more scattered growth pattern. The distinction matters because the management and risk profiles, while overlapping, are not identical.
Compared to LCIS, ALH represents the milder end of a spectrum that pathologists group together as “lobular neoplasia.” Both share the same cellular features, the same loss of cell adhesion proteins, and the same general risk profile. LCIS simply involves more of the lobular unit and carries a higher relative risk, estimated at 8 to 10 times the baseline. Think of ALH and LCIS as different points on a continuum rather than entirely separate diagnoses.
Risk Reduction Options
Because ALH increases breast cancer risk over a long time horizon, some women choose to take risk-reducing medication. Hormonal therapies that block estrogen’s effect on breast tissue can lower the risk of developing estrogen-receptor-positive breast cancer. These medications are typically taken for five years and are most beneficial for women at higher overall risk. The decision to start one involves weighing the potential benefit against side effects, which can include hot flashes, joint pain, and a small increase in the risk of blood clots or uterine changes depending on the specific medication.
Not everyone with ALH needs or wants to take medication. For many women, the combination of enhanced screening and close monitoring is a reasonable approach. The goal is early detection if cancer does develop, and modern imaging is highly effective at catching breast cancers at a treatable stage. Your overall risk profile, including age, family history, and whether ALH was found alongside other concerning features, shapes which strategy makes the most sense.