Microcystic adnexal carcinoma (MAC) is a rare, malignant sweat gland cancer with only 300 cases reported worldwide annually  . It most often occurs in women, between the ages of 50 to 70, although it has been reported in young children. The large majority of cases occur in whites, however, it has also been seen in Latinos and Asians with only a few cases in African Americans.
MAC shows up as a small tumor, usually on the face or neck. It is often in the center of the face. It looks like a small bump or slightly raised patch of skin. It can be flesh-colored or may have a yellowish color. It is often misdiagnosed, according to a study published in the journal Dermatology, it is misdiagnosed 30 percent of the time .
The tumor can increase in size, if not treated, however, the more dangerous, is that the tumor will spread inward, invading bone, muscles, blood vessels, cartilage and nerves located behind the tumor. The tumor, however, stays local and rarely metastasizes to different areas of the body.
It is usually painless and may be present for many years before treatment is sought. This may happen after the tumor begins to grow inward, causing numbness or tingling when it grows on the nerves.
Because the tumor most often occurs in whites and in areas that are most exposed to the sun (the face), sun exposure is thought to contribute to the onset of microcystic adnexal carcinoma. It often is found on the left side of the face, the part of the face that would be exposed to the sun while driving. However, somewhere between 20 percent and 50 percent of those with MAC also had previous radiation treatment for a previous condition, therefore, this may also contribute to the development of the tumor.
For most cases, surgery to excise the tumor is the best treatment. Mohs surgery has not been found to be more effective than simple excision. For some, radiation is used, either because surgery is not an option or along with surgery. However, complications from radiation include more frequent recurrence of the cancer. Radiation, as noted in the previous section, is also suspected as one of the causes of this type of cancer. Therefore, it is not considered as a first-line treatment.
"Microcystic Adnexal Carcinoma," Reviewed 2012, July 12, Staff Writer, Office of Rare Diseases Research, National Institutes of Health
"Microcystic Adnexal Carcinoma," 2000, Nov., Katarina Chiller, M.D. et al, Dermatology
"Microcystic Adnexal Carcinoma Clinical Presentation, 2012, July 11, Nektarios I. Lountzis, Medscape