Atypical hyperplasia of the breast is a condition in which breast tissue enlarges and overgrows. In itself, atypical hyperplasia is benign but if you have it, you may have a slightly increased risk of developing breast cancer in the future. If you have areas of atypical hyperplasia you may require surgery to remove it and to reduce the risk of developing malignant breast cancer.

What does ‘atypical hyperplasia’ mean?

The word ‘hyperplasia’ literally means an unusual increase in the number of cells present in any tissue. Hyperplasia can happen as a normal part of the ageing process. In the breast, hyperplasia starts when normal cells within the breast tissue begin to increase in number and/or get bigger. This can happen within either the ducts, which carry milk to the nipple when the breast is producing milk, or the lobules, the milk-producing glands.

In atypical hyperplasia, cells that increase in number also start to look abnormal, or atypical. Again, this can occur in either the ducts, when it is then called ductal atypical hyperplasia, or the lobules, when it is called lobular atypical hyperplasia. Around 5% of breast lumps show signs of atypical hyperplasia but very few turn out to be breast cancer.

What are the causes and symptoms of atypical hyperplasia?

It is not known exactly what causes atypical hyperplasia. It can sometimes arise in women with ductal papilloma. These are benign wart-like growths that sometimes develop in the ducts of the breasts, near to the nipples.

If you have atypical hyperplasia you don’t generally get any symptoms and the areas of excess breast tissue may not be large enough to notice. The condition isn’t painful and may only be discovered by chance or as part of routine breast screening.

Atypical hyperplasia and breast cancer risk

Women need to be aware of atypical hyperplasia because there is a chance that the abnormal breast cells might spread to the surrounding tissue, and this slightly increases the risk of developing breast cancer. In some cases, when cells within the lobules become particularly unusual, lobular atypical hyperplasia can develop into a pre-cancerous condition known as lobular carcinoma in situ (LCIS). This is not a true breast cancer, but is recognised as an ‘in-between’ stage.

How is atypical hyperplasia detected and diagnosed?

Because they don’t tend to cause any symptoms, hyperplasia and atypical hyperplasia are usually found by chance during routine breast cancer screening. Some women notice a suspicious area in their breast, which they naturally assume is something to worry about, and are then referred to a breast cancer specialist for further tests. These can include a mammogram or ultrasound scan.

If the tests identify an area of increased growth, a biopsy will usually be taken so that the cells of the area can be viewed under a microscope. A histologist will be able to give a firm diagnosis of atypical hyperplasia by examining the appearance of the cells.

Your specialist may also suggest an MRI scan or surgical removal of the abnormal breast tissue. Some women need to have a further biopsy of the area to screen for LCIS or signs of invasive breast cancer. 

Does atypical hyperplasia require any treatment?

Hyperplasia involving normal breast tissue doesn’t require any treatment but you might need a small operation to remove the affected area and reduce your future breast cancer risk.

You will also need to attend regular check-ups at your local breast clinic and undergo more frequent mammograms compared to women whose breasts have never shown any signs of hyperplasia.

It is important to remember that, while atypical hyperplasia is linked with a slightly increased risk of developing breast cancer in the future, this does not mean that it will happen to everyone with atypical hyperplasia. It is important to attend all of your follow-up appointments and to remain breast aware in the future, but not to worry unnecessarily.

In some cases, where the risk of developing breast cancer is thought to be particularly high, possibly due to the presence of other risk factors such as family history, you may need further risk reduction treatment. You might be prescribed a preventative medicine such as tamoxifen, and advised to avoid hormone replacement therapy or herbal menopause treatments that can increase breast cancer risk.

In the small number of extremely high-risk cases where genetic tests show you have a mutation in one of the known breast cancer genes, you might be offered a prophylactic mastectomy. This surgery will remove one or both breasts to take away all of the glandular tissue to prevent breast cancer developing there.