What is a Proliferating Adnexal Tumor

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An adnexal tumor is a new growth on a structure (called appendages) that is attached to another main or more important structure. This is a broad term for tumors that may develop in the structures attached to the skin, uterus or the eye. However, most proliferating adnexal tumors refer to malignancies of the skin appendages such as hair follicles, sweat glands and oil glands. Since these microscopic structures lie close to each other in the skin, there can be mixed tumor types where more than one structure is affected by cancer.

What are Skin Adnexal Tumors?

Skin adnexal tumors (SATs) are new growths involving the skin appendages, namely :

  • the hair follicles (trichilemmal tumors or cysts)
  • the sweat glands (apocrine and eccrine tumors)
  • the oil glands (sebaceous tumors)

As skin appendages, hair, sweat and oil glands are scattered all over the body, although more are found in the scalp, axilla (armpits), the extremities, the genitals, the anus, the chest, and around the nipples. Therefore, tumors may be found more in these areas. Other parts of the body that may be affected are the eyelids, the outer ears and the breast.

Most SATs are slow growing, benign or not life threatening and are confined to a small area (localized). However, in rare cases they may begin to proliferate or grow abnormally fast and changes in cell structures are seen as cancerous or malignant. They may be locally invasive but can also spread to the lymph nodes and distant organs like the lungs, bone and liver. These tumors may also be primary new growths or they may be a result of another cancer in the body that has metastasized or spread distantly.

Proliferating adnexal tumors are very rare, composing only 0.005% of all skin tumors. They are usually found in middle aged and older women, but some are also found in men and children. They may be asymptomatic and initially appear as a small painless bump with no other significant skin changes.


Diagnosis is made by taking a biopsy of the tumor to demonstrate the type of cells that are proliferating, and to distinguish the benign from malignant lesions. Often it is difficult to make definite classifications of the adnexal tumors because of the variety of morphologies in these structures. However, it is important to make an accurate diagnosis because many of these skin adnexal tumors are associated with other internal malignancies and syndromes. For example, trichilemmomas are part of Cowden disease and sebaceous tumors are part of a disease entity called Muir–Torre syndrome.


These malignancies are usually aggressive and can recur despite surgical treatment. Surgical removal involves wide excision of the lesion, meaning that aside from the tumor a margin of normal tissue around the tumor is also removed. This is done to prevent recurrence of the tumor.


Prognosis is based on the size, extent and other organs involved in the growth of these tumors. Since they are often long-standing tumors with very little clinical manifestations, they may be diagnosed late and if the malignancy has spread, prognosis may be poor.


KnowCancer.com, “Adnexal And Skin appendage Neoplasms” accessed 12/23/10


J Clin Pathol , “Troublesome tumours 1: Adnexal tumours of the skin” accessed 12/23/10


J Clin Pathol , “Skin adnexal neoplasms—part 1: An approach to tumours of the pilosebaceous unit”