Microcystic adnexal carcinoma (MAC) is a rare malignant sweat gland tumor that commonly occurs on the head and neck.MAC has a predilection for the central face, but may be found although it may be found on the trunk, axilla, extremities, and genitals. MAC is characterized by its slow growth but local aggressiveness.
There are approximately 200 cases worldwide; however, it was Goldstein and others that first described MAC in 1982.
MAC has been mentioned under a number of names including:
The tumor, known as syringomatous adenoma of the nipple, has been considered MAC; however, this is debated. MAC is known to have perineural invasion (upwards of 80%) with infiltration beyond clinically apparent margins. However, it has little metastatic potential but often recurs.
Risk factors have been identified for forming MAC:
The estimate for the link to therapeutic radiation ranges from 19% to 50%, with an average latent period of 30 to 40 years. UV radiation is often implicated due to the fact that most lesions appear in sun-exposed areas and those with Fitzpatrick skin types I and II.
Microcystic adnexal carcinoma has also been reported in younger individuals with a history of additional UV exposure, such as fighter pilots.
The effect of immunosuppression on the risk for the development of MAC is unclear at this time, although immunosuppression increases the risk of basal cell carcinoma and squamous cell carcinoma.
MAC tends to occur in adults 55 to 60 years old. However, it occasionally has occurred in children. Microcystic adnexal carcinoma arises equally in males and females although some literature lists a slight female predominance.
Microcystic adnexal carcinoma often grows slowly and will present as a white to pink plaque located on the face. Often, it has been overlooked or ignored. Often it is confused with a basal cell carcinoma clinically. In such an instance, a shave biopsy is usually performed. However, in the case of microcystic adnexal carcinoma, the pathology lies deeper than a superficial shave biopsy will show. Thus, making the diagnosis more difficult. If suspected, a punch biopsy should be performed.
Histologically, MAC can mimic infiltrative/morpheaform basal cell carcinoma, desmoplastic squamous cell carcinoma, desmoplastic trichoepithelioma, trichoadenoma, and syringoma.
Histopathological examination reveals small basaloid cells/keratocysts on the top, hence the term “microcystic.” This is a key feature. On higher power, one can see cords and strands of basaloid epitheloid cells displaying ductal lumina that invade the dermis and subdermis. There is also fibrotic stroma. A key feature in distinguishing MAC from other tumors is a zone of separation between the epidermis and tumor. Additionally, the ductal structures distinguish MAC from desmoplastic trichoepithelioma and trichoadenoma.
MAC is distinguished from morpheaform basal cell carcinoma and desmoplastic squamous cell carcinoma on the basis of ductal differentiation.
Microcystic adnexal carcinoma is a solitary white to pink plaque located on the face or trunk. In the case of early tumors, the appearance may be slightly elevated; however, a more nodular appearance tends to develop with time.
MAC often may be clinically indistinguishable from other skin-colored growths on the head and neck. MAC may have perineural spread where patients can complain of numbness, tingling, pain, burning, and itching sensations. The key to
diagnosis is taking an appropriate pathology specimen is needed, and the key to diagnosis. The tumor largely lies within the deep dermis. A superficial biopsy can lead to an incorrect diagnosis. If MAC is suspected, avoid a superficial shave biopsy.
An incisional biopsy is recommended in the evaluation. However, punch biopsies and excisional biopsies are options in evaluation.
Full Skin Examination
Consider the need for imaging (CT or MRI) or fat-suppression MRI protocol for perineural invasion or intraorbital tumors.
Dermoscopy does not offer a definitive diagnosis of MAC. MAC is a rare tumor, so dermoscopic findings are limited to case reports with the most characteristic finding appears to be the presence of whitish clods of variable size. These whitish clods likely representing keratinous cyst. MAC can appear like a basal cell carcinoma due to the presence of arborizing vessels reported in case literature.
MAC is managed surgically by simple excision or Mohs micrographic surgery (MMS). Complication rates between MMS and simple excision are similar. When utilizing MMS, clear margins were obtained in fewer procedures and resulted in fewer office visits.
In the event that Mohs micrographic surgery is not an option due to lack of procedure availability or tumor extent, intraoperative frozen sections may be useful for guiding conventional surgical excision.
Patients should be followed every six to twelve months following diagnosis and management for full-body skin examination and lymph node examination.
MAC presents often on the face as a papule or plaque. The differential can be large. However, the differential diagnosis where MAC must be distinguished from is morpheaform basal cell carcinoma, desmoplastic squamous cell carcinoma, desmoplastic trichoepithelioma, trichoadenoma, and syringoma.
The role of radiation therapy for microcystic adnexal carcinoma remains unclear. Monotherapy with radiotherapy is not recommended. According to the latest evidence-based clinical practice guidelines for MAC, adjuvant radiotherapy can be considered for MAC when there is peripheral nerve involvement, when margins and unable to be cleared surgically, or when there is tumor present at the margins. Although, there have been reports of chemoradiation with carboplatin/paclitaxel combination used in a patient refusing surgical management that remained tumor-free for six years.
Prophylactic radiotherapy of the sentinel node base is not supported by current evidence.
The major prognostic concern for MAC is the recurrence of the tumor. Recurrence is generally seen within two to three years; however, it may occur even decades later. MAC is a locally aggressive tumor whereas metastases are generally rare. Death may result from the invasion of vital structures.
Complications of untreated tumors are locally aggressive invasion. Depending on location, complications can result from the invasion of vital structures. In some instances, death has resulted.
Patients should be educated that MAC is a slow growing tumor. Patients should be educated on the importance of follow-up examinations, and that recurrence may even occur decades later in some instances.
Microcystic adnexal carcinoma is a malignant tumor of sweat gland origin found primarily on the head and neck. Appropriate biopsy technique is key in establishing the correct diagnosis. Mohs micrographic surgery should be considered first-line surgical management in its ability to analyze the entire surgical margin intraoperatively.
Microcystic adnexal carcinoma frequently poses a diagnostic dilemma. These patients may note a long history of a papule or plaque on the head and neck. Physical examination of the skin may reveal tumor present; however, accurate diagnosis depends on proper biopsy technique with a raised index of suspicion. While a dermatologist is almost always involved in the care of patients with microcystic adnexal carcinoma, it is important to consult with an interprofessional team of specialists that include a Mohs surgeon, an otolaryngologist and possibly radiologist. Nurses are also vital members of the interprofessional group as they will assist with the education of the patient and family. In the postoperative period for pain and wound infection, the pharmacist will ensure the patient is on the right analgesics and antibiotics. The radiologist plays a vital role in determining the extent of involvement, perineural invasion, and presence of intraorbital tumors. Clinical practice guidelines have been established in dermatology literature developed following an exhaustive review of current medical literature from peer-reviewed journals to determine appropriate management based upon current evidence. [Level 1]
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