Hidradenoma

by Jason Wasserman MD PhD FRCPC
November 25, 2024

A hidradenoma is a non-cancerous skin tumour arising from the sweat glands within the skin. These tumours are relatively rare and can develop anywhere on the body. They are most commonly found on the trunk (chest, back, and abdomen) and extremities (arms and legs). Hidradenomas are typically slow-growing and present as small, firm, painless lumps beneath the skin.

What are the symptoms of hidradenoma?

The symptoms of a hidradenoma can vary depending on its size and location. Common symptoms include:

• A small, firm lump under the skin: Hidradenomas usually appear as a painless bump ranging from a few millimetres to several centimetres.
• Slow growth: These tumours typically grow gradually over time and may not cause noticeable symptoms initially.
• Tenderness or pain: In some cases, particularly if the tumour grows large or becomes irritated, it can cause mild discomfort or tenderness.
• Skin changes: The skin over the tumour may appear normal, but in some cases, it may become stretched, reddened, or slightly raised.
• Ulceration or drainage: Rarely, the tumour may break through the skin, leading to ulceration or fluid discharge.

What causes a hidradenoma?

Most hidradenomas are associated with a genetic change called a fusion involving the genes CRTC1 and MAML2. This fusion results in abnormal growth of the sweat gland cells, leading to tumour formation. Although this genetic change has been identified, the exact reason why it occurs is not fully understood. It is not typically inherited or linked to any specific environmental factors.

Do hidradenomas need to be removed?

Although hidradenomas are non-cancerous, they are typically removed for several reasons:

• Continued growth: These tumours can slowly increase in size, which may cause discomfort or cosmetic concerns.
• Accurate diagnosis: Complete removal allows for a thorough pathological examination to confirm the diagnosis and rule out other conditions.

While hidradenomas do not transform into cancer over time, surgical removal is often recommended for symptom relief, cosmetic reasons, or to ensure proper diagnosis.

How is this diagnosis made?

A pathologist typically makes the diagnosis of hidradenoma after the tumour has been removed and examined under a microscope. In most cases, the entire tumour is surgically removed through a procedure called excision, which provides enough tissue for a definitive diagnosis. Alternatively, a small portion of the tumour may be removed in a procedure called a biopsy. The tissue is then analyzed in a laboratory, where the pathologist identifies characteristic features of hidradenoma, confirming the diagnosis and distinguishing it from other types of skin tumours.

Margins

A margin refers to the tissue the surgeon cuts to remove the tumour. The pathologist carefully examines margins to ensure that all tumour cells have been removed. There are two possible outcomes for margin assessment:

• Negative margin: This means no tumour cells are at the edge of the removed tissue. A negative margin suggests that the entire tumour has been successfully removed, and the risk of the tumour growing back is low.
• Positive margin: This means tumour cells are present at the edge of the removed tissue. A positive margin increases the risk of the tumour recurring (growing back) at the same site. Further treatment, such as additional surgery, may be recommended if this occurs.