AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

Background

Microcystic adnexal carcinoma (MAC) is a rare, malignant appendage tumor commonly classified as a low-grade sweat gland carcinoma that typically occurs on the head and neck, particularly the central face. It shows aggressive local invasion but has little metastatic potential. Goldstein et al¹ described the first series in 1982, emphasizing the importance of its distinction from the benign histologic mimics termed syringoma, desmoplastic trichoepithelioma, and trichoadenoma.

Despite subsequent widespread recognition of MAC as a discrete clinicopathologic entity, its precise relationship to and histologic discrimination from other putative locally aggressive sweat gland carcinomas (reported under a variety of names, including sclerosing sweat duct carcinoma, syringoid eccrine carcinoma, syringomatous carcinoma, and eccrine epithelioma) remains unresolved and has provoked considerable nosologic and diagnostic confusion. The authors regard MAC as synonymous with group 1 sclerosing sweat duct carcinomas as described by Cooper et al.² In addition, the tumor described as syringomatous adenoma of the nipple is regarded by some authorities as MAC.

The Medscape Skin Cancer Resource Center may be of interest, as may the eMedicine article Eccrine Carcinoma.

Pathophysiology

The differentiation pathway of MAC has provoked considerable debate. Goldstein et al¹ initially suggested that it showed dual pilar (the superficially located keratocysts resembling follicular infundibula) and eccrine differentiation. Others have supported this notion noting, in particular, that the keratocysts often expressed pilar-type keratins and that, occasionally, trichohyalin granules are present. However, some authors have suggested that MAC shows only eccrine differentiation.

More recently, based on the ontogenetic relationship between hair follicles and apocrine glands, MACs have been theorized to display folliculo-apocrine or sometimes folliculo-sebaceous-apocrine differentiation rather than folliculo-eccrine differentiation. Support for this premise is provided by occasional cases showing focal apocrine decapitation secretion and the demonstration of sebaceous foci in some tumors.

Little information is available on the molecular pathophysiology of MACs, although 1 report documented a deletion on arm 6q in 1 case. A case of MAC occurring in siblings also suggests a genetic role.³

Frequency

United States

MAC is a rare tumor, with only slightly more than 300 cases reported worldwide.⁴ Thomas et al⁵ reported a mean number of 1.63 cases per year in a rural northeastern area of the United States.

Mortality/Morbidity

Morbidity is high because of the deeply infiltrating nature of the tumor, which can invade into bone, muscle, blood vessels, cartilage, and nerves. In one study, the mean clinical lesion size was 3 cm², but the final defect size was 18 cm², highlighting its occult extension.⁵

Metastatic disease is rare, with only 5 local^{6, 7, 8, 9, 10} and 3 distant metastases reported.^{11, 12, 13} Despite this, and considering that more than 300 cases have reported in the medical literature worldwide,⁴ only 1 death has been attributed to MAC,¹⁴ which was a case of metastatic disease.  

One case reported a high-grade carcinosarcoma with an architectural pattern similar to MAC but also exhibiting nuclear pleomorphism, hyperchromasia, and large nucleoli. The patient developed metastatic lung disease and died within 6 months.¹⁵ The authors further noted histologic high-grade features in their case that were similar to other cases reported with metastatic disease,^{10, 12, 14} and they suggested this may be a indicator for more aggressive disease. Whether this represents an undefined adnexal carcinoma with an architectural pattern similar to MAC or a morphological variant of MAC with high-grade histologic features remains unknown.

Race

Most cases of MAC occur in whites, but 5 cases have been reported in African Americans^{4, 14, 16, 17, 18} and 1 case has been reported in a Japanese woman.¹⁹

Sun exposure may play less of a role in persons of nonwhite ethnic origin, with one lesion occurring on the vulva of an African American woman,¹⁷ multiple lesions occurring on the trunk and extremities (with sparing of the face) in an African American man,⁴ and 1 occurring in the perianal region in a Japanese woman.¹⁹

The other reported cases in African Americans occurred on the scalp^{16, 18} and upper cutaneous lip,¹⁴ where sun exposure is prominent.

Sex

No significant sexual predilection is reported, although some studies suggest a slight female predominance.^{3, 20, 21}

Age

MAC may manifest at any time from the second to the eighth decade of life, with most patients in their 40s, 50s, or 60s.^{3, 22} In one series of cases, the mean age was found to be slightly higher (70 y).⁵ The age range is broad. MAC has been reported in an 11-year-old year-old boy²³ and a 90-year-old person.²²

CLINICAL

Section 3 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

History

• MAC has an indolent onset, manifesting as an indurated plaque or nodule, often present for many years.
• It is usually asymptomatic, but it may be painful.
• Numbness or paresthesia may be present in patients with perineural infiltration.

Physical

• Appearance: MACs are flesh colored, yellow, or erythematous.
• Morphology
• • The most common forms are indurated plaques or nodules.
  • Cystlike tumors have also been reported.
  • The skin surface is usually smooth, but it may show hyperkeratosis.
• Location
• • The tumor is most commonly found in the head and neck region (85%), with a predilection for the nasolabial area (especially the upper lip) and the periorbital skin.⁵
  • A left-sided facial preponderance was noted in a large US study. Left-sided preponderance was considered to be the result of uneven UV exposure while driving (US steering wheels are placed on the left).
  • MAC has been found to occur in other locations, such as the upper extremity (8%), trunk (4%), and lower extremity (4%).⁵ Involvement of the axillae, the buttocks, the scalp, the vulva,¹⁷ and the genitalia²¹ is rare but has been reported. Lesions in non–sun-exposed sites may occur more often in persons of nonwhite ethic origin.
  • One case of multiple primary MACs (21 total) of the trunk and extremities in sun- and non–sun-exposed areas, with sparing of the face, has been reported.⁴
• Size
• • The average size is 1-3 cm in diameter,⁵ with the largest reported lesion measuring 12 cm in diameter.²⁴
  • The actual clinical size is difficult to determine because of the tendency for extensive subclinical involvement.

Causes

• Therapeutic radiation (radiation therapy): Approximately 10% of patients have had treatment with radiation therapy for a previous condition. The average latency period is 30 years.
• UV radiation: Long-term UV exposure has also been postulated as a predisposing factor for MAC, especially in view of its predilection for sun-exposed sites (ie, favoring the left side of the face, owing to suspected sun exposure while driving) and the skin of white persons.

DIFFERENTIALS

Section 4 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

Other Problems to be Considered

Desmoplastic trichoepithelioma
Squamous cell carcinoma (poorly differentiated)
Adenosquamous carcinoma
Eccrine epithelioma
Morpheaform basal cell carcinoma
Trichoadenoma
Cutaneous metastases of breast carcinoma
Other metastatic adenocarcinomas

WORKUP

Section 5 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

Imaging Studies

CT scanning may be used to map out local invasion into nerves, muscle, cartilage, or bone, and it may also be used to help define metastatic disease, if suspected. MRI has also been used to assess tumor extent.¹² However, imaging is not necessary in most cases of microcystic adnexal carcinoma (MAC). 

Procedures

A deep incisional or excisional biopsy is required. Superficial biopsies lead to misdiagnosis because deep extension and perineural invasion are key features of the tumor.

Histologic Findings

MAC is a poorly circumscribed, deeply infiltrative, asymmetric tumor composed of variable proportions of keratocysts, squamoid or basaloid nests, infiltrating cords, and ductular structures set in a variably hyalinized but usually paucicellular desmoplastic stroma. The epithelial nests are tadpole shaped, creating a "paisley-tie" appearance. Lymphoid aggregates are common, particularly at the dermal-subcutaneous junction.

Hematoxylin and eosin

In a minority of cases, MAC shows attachment to the epidermis or the follicles, but generally,  a striking zonal separation is noted between the tumor and the epidermis. In the superficial aspects of the tumor, small-to-medium keratinizing cysts lined by squamous epithelium can be seen. Atypia and mitoses are sparse. Nests of small basaloid or squamoid cells, sometimes showing a whorled-appearing infiltrate between the cysts with depth, are present. These may be solid, show central keratinization, can rarely be calcified or demonstrate central lumen formation, and have a tadpole or paisley-tie appearance.

In deeper sections, variable numbers of small ducts lined by 1-2 layers of cuboidal cells are present throughout the tumor. Narrow cords of cuboidal cells usually characterize the deepest portion of the tumor. Some of the nests and ducts show tail-like cellular extensions reminiscent of syringoma. Glycogen-rich, clear-cell change, foci of decapitation secretion, and sebaceous cell or duct differentiation may be present. The nuclei of all the components are mainly small, slightly irregular, and hyperchromatic, but little pleomorphism or mitotic activity occurs. Perineural infiltration is common.    

With regard to histologic subtype, tumors displaying the architectural features of MAC but with increased nuclear pleomorphism, hyperchromasia, vascular invasion, and necrosis may be suggestive of a more aggressive subtype. Clinically, these have demonstrated rapid growth, carcinosarcomatous metaplastic transformation with relapse, and suspected metastases.¹⁵

Toluidine blue

Special staining with toluidine blue has been shown to highlight infiltrating tumor strands with a distinctive pink halo and perineural invasion with a maroon tint.²⁵ This stain may be of benefit in Mohs micrographic surgery (MMS). 

Immunohistochemistry

Pancytokeratin, AE1/AE3, and cytokeratin-1 positively highlight tumor cells. Reactivity to hard keratin subclasses AE 13 and AE 14 has been demonstrated and suggests pilar differentiation.²⁶ Epithelial membrane antigen and carcinoembryonic antigen highlight ductal structures or intracytoplasmic lumen formation and suggest sudoriferous differentiation. Additionally, Leu-M1 is positive and S-100 is negative.²⁶

Cytokeratin-20 tumor staining was negative in one case report.²⁸ Its utility was suggested to help differentiate MAC from other benign adnexal tumors that typically carry scattered Merkel cells throughout.

Histologic differential diagnosis

The important differentials histologically are syringoma and desmoplastic trichoepithelioma. With hematoxylin and eosin staining, attention to the infiltrative growth pattern, and, if present, perineural invasion, usually easily discriminates MAC from the others in suitable biopsy specimens. CD5 positivity in deeper sections would favor MAC over desmoplastic trichoepithelioma.   

That being stated, rendering a definitive diagnosis from a shave or superficial punch biopsy specimen often is impossible. Duct formation, if present, would favor MAC over desmoplastic trichoepithelioma. Further, keratocysts with mild atypia and little mitosis would favor MAC over syringoma.  Cytokeratin-20 testing for Merkel cell loss suggests MAC.²⁸

Distinction from a morpheaform basal cell carcinoma can be made by the demonstration of duct and intracytoplasmic lumen formation and with zonation of the tumor from the epidermis, which is typically seen with MAC. Ductal formation is rare in basal cell carcinoma. If seen, it is usually in nodular subtypes. CD5 positivity in deeper sections would also favor MAC over morpheaform basal cell carcinoma, whereas Ber-EP4 positivity favors basal cell carcinoma. 

Desmoplastic squamous cell carcinoma generally lacks zonation from the epidermis, ductal structures, or intracytoplasmic lumen formation.

Desmoplastic melanoma also typically lacks zonation, ductal structures, and keratocyst formation, and it is reliably S-100 positive. Lymphoid aggregates are usually situated throughout the tumor, as opposed to the dermal-subcutaneous junction, as is seen in MAC.

Trichoadenomas tend to be more well-defined tumors with larger keratin cysts surrounded by a fibrovascular stroma. Typically, they lack deep invasion and do not show perineural invasion.

Metastatic adenocarcinomas (ie, breast and colon) demonstrate more pleomorphism and cytologic atypia, and they lack keratocyst formation.

Most authorities distinguish MAC from similar low-grade sweat gland carcinomas that have previously been termed syringomatous carcinoma, eccrine epithelioma, or group 2 sclerosing sweat duct carcinoma largely on the basis of the presence of keratocysts or other evidence of follicular differentiation. However, some have suggested that these tumors could be variations of the same entity.

TREATMENT

Section 6 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

Medical Care

Surgery is the mainstay of treatment. Radiation therapy has also been used as a primary therapy²⁹ or as an adjuvant to surgery. However, radiation alone often results in recurrence (It is also implicated as a cause of microcystic adnexal carcinoma [MAC].) and some tumors are radioresistant.²⁹

Surgical Care

MMS is the current treatment of choice. Clinical margins are difficult to define, and MMS offers an excellent way of following the infiltrating nature of the tumor and tracing perineural involvement. The discrepancy between clinical and histologic extent can be marked, in that the size of the defect after complete tumor removal following MMS can be as much as 4²¹ to 6⁵ times that of the clinically apparent size. Therefore, standardized, predictable, predetermined surgical margins cannot be used in the treatment of MAC.

MMS versus simple excision 

In the largest series to date (48 patients), Chiller et al²¹ found little difference in the overall recurrence rate between tumors treated with MMS (2.4% per person-year) versus standard surgical excision (1.5% per person-year) at a mean follow-up of 3.2 years. However, MMS exhibited a clear benefit over simple excision in that 30% of tumors treated with simple excision required at least another office visit to clear the patient of histological tumor findings, with 1 patient still not tumor free after 4 simple excisions. This rate was compared with 0% if treated by MMS. A study by Abbate et al³ reported similar findings (MMS with 0 recurrences out of 4 cases vs excision with 1 recurrence out of 6 cases).

In a large prospective study of patients with MAC, only one case of recurrence was reported out of 20 (5%) at a 5-year follow-up period after MMS,³⁰ and a study by Friedman et al²⁰ with a similar follow-up period had no recurrence in 11 patients treated with MMS. Thomas et al⁵ found a 12% recurrence rate with a mean follow up of 3.3 years in their study, similar to the 10.3% recurrence rate and 2-year follow up noted by Snow et al.³¹ The overall recurrence rates for MMS range from 0-12%. Local recurrence rates of up to 30-47% have been reported with standard surgical excision. Recurrences have also been noted from 5 months to 30 years after excision; thus, longer follow-up is necessary to fully assess both treatment modalities.

Some have suggested the use of an additional layer after complete clearance of margins with MMS for further histologic control.^{19, 32} No outcome data exists on this technique.

Staged excision (slow MMS)  

Problems can also be encountered in interpreting frozen sections during MMS, when microscopic invasion can be elusive. Barlow et al³³ proposed that delayed-closure MMS using formalin-fixed, paraffin-embedded specimens improves the histologic assessment and decreases the risk of missing a strand of tumor. Some advocate the use of tangential frozen sections with MMS plus formalin-fixed paraffin sections for the final layer, and this is a workable compromise. Moreover, recent reports advocate the use of toluidine-blue staining on frozen sections to highlight MAC extension. Tumor stroma has a pink halo, owing to the presence of mucopolysaccharide and hyaluronic acid, and perineural involvement has a magenta hue, thereby augmenting visualization and clearance with MMS.²⁵

FOLLOW-UP

Section 7 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

Further Outpatient Care

The longest latent period for microcystic adnexal carcinoma (MAC) recurrence following simple excision is 30 years. This particular patient underwent a simple excision for adnexal adenoma in 1953. When he presented again 30 years later, the initial slides were reviewed, and a retrospective diagnosis of MAC was made. This case illustrates the indolent nature of MAC and supports the view that simple excision may be not adequate and long-term follow-up care is required.

Deterrence/Prevention

Sun avoidance minimizes UV exposure, which may be a predisposing factor.

Complications

Local recurrence is a complication if it is not properly excised. Additionally, because of the deep penetration of the tumor, destruction of underlying tissue (eg, bone, cartilage, muscle) can lead to structural changes and increased morbidity.

Prognosis

Overall, the prognosis is good, especially when margin-control techniques such as MMS are used, with a modest tendency for recurrence and a very low rate of metastases.  

The largest series reports an overall (combining results from simple excision and MMS) 10-year recurrence rate of 18%.  Others have reported a 12% recurrence rate at mean follow-up of 39 months.⁵ 

Although MAC is considered a nonmetastasizing tumor, rare reports detail histologically confirmed lymphatic spread. Of the more than 300 reported cases of MAC, only 8 have been metastatic.^{6, 7, 8, 9, 10, 11, 12, 13}

One death has been attributed to metastatic MAC. The patient presented with mediastinal lymphadenopathy and later died of the disease. However, no histologic evidence from the lymph nodes confirmed the cause of death.¹¹ In another reported case of distant metastatic disease, the patient eventually died of aspiration pneumonia, not from the MAC itself.¹²

MISCELLANEOUS

Section 8 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

Medical/Legal Pitfalls

Ensuring that the biopsy specimen is adequate for diagnosis and that the histopathologist is aware of this entity is important because as many as 30-85% of cases of MAC are misdiagnosed.^{13, 30}

ACKNOWLEDGMENTS

Section 9 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

The authors and editors of eMedicine gratefully acknowledge the contributions of previous author, Kevin Hollowood, MD, MBBS, MRCP, FRCPath, to the development and writing of this article.

MULTIMEDIA

Section 10 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

Media file 1:  Clinical photo of a microcystic adnexal carcinoma on the left upper lip of an elderly woman. Note the close resemblance to basal cell carcinoma. Courtesy of Dirk M. Elston, MD.
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Media type:  Photo

Media file 2:  A low-power view of microcystic adnexal carcinoma demonstrates superficially located keratocysts and variably sized tumor nests and ducts. Note the diminution in size of the nests and cysts with the depth of dermal invasion. Courtesy of Dirk M. Elston, MD
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Media type:  Photo

Media file 3:  Small ductular structures lined by 2-3 cell layers of small eosinophilic cells showing little pleomorphism set in a dense fibrous stroma. Courtesy of Dirk M. Elston, MD.
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Media type:  Photo

Media file 4:  A high-power view of small, irregularly shaped nests and strands of small tumor cells without obvious ductal formation. Courtesy of Dirk M. Elston, MD.
	View Full Size Image
Media type:  Photo

REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Acknowledgments
• Multimedia
• References

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34. Antley CA, Carney M, Smoller BR. Microcystic adnexal carcinoma arising in the setting of previous radiation therapy. J Cutan Pathol. Jan 1999;26(1):48-50. [Medline].
35. Burns MK, Chen SP, Goldberg LH. Microcystic adnexal carcinoma. Ten cases treated by Mohs micrographic surgery. J Dermatol Surg Oncol. Jul 1994;20(7):429-34. [Medline].
36. Kumar K, McGregor JC, Watson JD. Microcystic adnexal carcinoma: a report of three cases. J R Coll Surg Edinb. Dec 1998;43(6):412-4. [Medline].
37. LeBoit PE, Sexton M. Microcystic adnexal carcinoma of the skin. A reappraisal of the differentiation and differential diagnosis of an underrecognized neoplasm. J Am Acad Dermatol. Oct 1993;29(4):609-18. [Medline].
38. Lupton GP, McMarlin SL. Microcystic adnexal carcinoma. Report of a case with 30-year follow-up. Arch Dermatol. Mar 1986;122(3):286-9. [Medline].
39. McCalmont TH. A call for logic in the classification of adnexal neoplasms. Am J Dermatopathol. Apr 1996;18(2):103-9. [Medline].
40. Nagatsuka H, Rivera RS, Gunduz M, Siar CH, Tamamura R, Mizukawa N, et al. Microcystic adnexal carcinoma with mandibular bone marrow involvement: a case report with immunohistochemistry. Am J Dermatopathol. Dec 2006;28(6):518-22. [Medline].
41. Nickoloff BJ, Fleischmann HE, Carmel J, Wood CC, Roth RJ. Microcystic adnexal carcinoma. Immunohistologic observations suggesting dual (pilar and eccrine) differentiation. Arch Dermatol. Mar 1986;122(3):290-4. [Medline].
42. Reqena L, Kiryu H, Ackerman AB. Neoplasms With Apocrine Differentiation. Philadelphia: Lippincott-Raven: 1998.
43. Sabhikhi AK, Rao CR, Kumar RV, Hazarika D. Microcystic adnexal carcinoma. Int J Dermatol. Feb 1997;36(2):134-6. [Medline].
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Article Last Updated: Nov 12, 2008