ADNEXAL CARCINOMA
Adnexal
carcinomas are a diverse group of malignant skin tumors that are derived from
the various components of the skin appendageal structures. These tumors are
extremely rare and comprise well less than 1% of all skin cancers diagnosed
annually. They are difficult to diagnosis clinically because they can all mimic
the more common types of skin cancer, particularly basal cell carcinoma and
squamous cell carcinoma. They can be diagnosed with certainty only after
histological examination. These tumors are believed to be derived from hair
follicle, sebaceous gland, apocrine gland, or eccrine gland epithelium. They
are thought to arise de novo and can also arise from a preexisting benign
precursor. An example is an eccrine porocarcinoma developing within an eccrine
poroma.
Clinical Findings: These tumors are very rare, and one is unlikely to
consider them in the differential diagnosis when evaluating an individual with
an undiagnosed skin growth. There are few clues to their origin, which makes
diagnosis of these cancerous tumors almost impossible based on clinical
findings alone. Most manifest as a solitary papule, plaque, or dermal nodule.
Most are asymptomatic, but pruritus, bleeding, and pain may be present.
The diagnosis of these tumors requires
tissue sampling. A punch or excisional biopsy is the best method to biopsy
these lesions, because it allows the pathologist to get a large enough piece of
tissue to evaluate. A punch biopsy is especially important to help
differentiate microcystic adnexal carcinoma from a benign syringoma. The latter
is very superficial in nature, whereas the microcystic adnexal carcinoma
displays a deep infiltrative growth pattern that will not be appreciated with a
superficial shave biopsy.
Pathogenesis: The pathogenesis of these tumors is poorly
understood. In contrast to basal and squamous cell carcinomas, they are
unlikely to be caused by ultraviolet light exposure. The rarity of the tumors
makes them difficult to study. There appears to be no genetic inheritance to
these malignant tumors, with the lone exception of the sebaceous carcinoma.
Sebaceous carcinoma can be seen in the Muir-Torre syndrome, which is inherited
in an autosomal dominant pattern.
Histology: Each tumor is unique histologically. The tumors
can be subdivided according to the type of epithelium from which they are
derived: sebaceous, hair follicle, eccrine, or apocrine. The pathologist is
able to differentiate these tumors based on certain criteria. The tumors show
varying amounts of cellular atypia and an invasive growth pattern. They are
usually poorly circumscribed with varying amounts of mitotic figures, necrosis,
and abnormal-appearing cells. Various gland-like structures can be seen in some
tumors, which can be helpful in making the diagnosis. Often, special
immunohistochemical stains are used to help differentiate the subtypes of these
tumors.
Treatment: These tumors should all be surgically excised with
clear surgical margins. The Mohs surgical technique has been used successfully
to treat these tumors, as has a standard wide local excision. Sentinel node
removal and evaluation is not routinely performed, but some clinicians advocate
its use, especially in some of the more aggressive subtypes such as the eccrine
porocarcinoma. Sentinel node removal and evaluation has not shown any survival
benefit to date. Mohs surgery may lead to a decrease in recurrence rate and is
tissue sparing. Because of the rare nature of these tumors and the lack of
prospective randomized studies, it is difficult to determine the best removal
method. For the same reasons, the ultimate prognosis and the recurrence rate of
these tumors are unknown. After diagnosis and removal of these tumors, the
patient should have long-term follow-up to evaluate for recurrence.
Adnexal tumors that have metastasized
are treated with chemotherapy with or without radiotherapy. The prognosis is
poor for patients who develop metastatic adnexal carcinoma.
