Muir-Torre syndrome

Muir-Torre syndrome (MTS) is a form of Lynch syndrome and is characterized by sebaceous (oil gland) skin tumors in association with internal cancers.^[1][2][3] The most common internal site involved is the gastrointestinal tract (with almost half of affected people having colorectal cancer), followed by the genitourinary tract. Skin lesions may develop before or after the diagnosis of the internal cancer.^[1] MTS is caused by changes (mutations) in the MLH1 or MSH2 genes and is inherited in an autosomal dominant manner.^[2] A mutation in either of these genes gives a person an increased lifetime risk of developing the skin changes and types of cancer associated with the condition.^[3]

Sebaceous adenoma is the most characteristic finding in people with Muir-Torre syndrome (MTS). Other types of skin tumors in affected people include sebaceous epitheliomas, sebaceous carcinomas (which commonly occur on the eyelids) and keratoacanthomas. Sebaceous carcinoma of the eyelid can invade the orbit of the eye and frequently metastasize, leading to death. Tumors at other sites can also metastasize, but are less likely to cause death. Common sites of keratocathomas include the face and the upper side of the hands, but they can occur anywhere on the body.^[4]

The most common internal cancer in people with MTS is colorectal cancer, occurring in almost half of affected people. The second most common site is the genitourinary tract. Other cancers that may occur include breast cancer, lymphoma, leukemia (rarely), salivary gland tumors, lower and upper respiratory tract tumors, and chondrosarcoma. Intestinal polyps as well as various benign tumors may also occur.^[4]

Muir-Torre syndrome is a subtype of Lynch syndrome and may be caused by changes (mutations) in either the MLH1, MSH2, or MSH6 gene.^[2][5] These genes give the body instructions to make proteins needed for repairing DNA. The proteins help fix mistakes that are made when DNA is copied before cells divide. When one of these genes is mutated and causes the related protein to be absent or nonfunctional, the number of DNA mistakes that do not get repaired increases substantially. The affected cells do not function normally, increasing the risk of tumor formation. The MSH2 gene is responsible for MTS in the majority of cases.^[4][6] Mutations in MLH1 and MSH2 have the most severe effect.^[5]

Not everyone diagnosed with MTS will have a detectable mutation in one of these genes.^[3] Other, unidentified genes may also play a role in the development of the condition.

A person is suspected to have Muir-Torre syndrome (MTS) if he/she has one or more of the following:

• History of one or more sebaceous tumors
• Age younger than 60 years at first presentation of sebaceous tumors
• Personal history of Lynch-related cancers
• Family history of Lynch-related cancers^[5]

The presence of specific skin tumors in MTS may lead to the correct diagnosis even in the absence of a clear family history. A person diagnosed with MTS can also have genetic testing to see if they have a mutation in one of the genes known to cause MTS. However, not everyone with Muir-Torre syndrome will have a detectable mutation in one of these genes.^[3] Other, unidentified genes may also play a role in the development of the condition.

Muir-Torre-syndrome (MTS) is a variant of Lynch syndrome and is inherited in an autosomal dominant manner. This means that having only one changed (mutated) copy of the responsible gene in each cell is enough for a person to develop the condition. When a person with an autosomal dominant condition has children, each child has 50% (1 in 2) chance to inherit the mutated copy of the responsible gene. It is important to note that people who inherit a mutated gene that causes MTS inherit an increased risk of cancer, not the disease itself. Not all people who inherit a mutation in an associated gene will develop cancer. This phenomenon is called reduced penetrance.

The majority of people diagnosed with a form of Lynch syndrome have inherited the mutated gene from a parent. However, because not all people with a mutation develop cancer, and the variable age at which cancer may develop, not all people with a mutation have a parent who had cancer.^[7] Thus, the family history may appear negative. A positive family history of MTS is identified in roughly 50% of affected people.^[4] The percentage of people with Lynch syndrome who have a new mutation in the gene that occurred for the first time (and was not inherited from a parent) is unknown but is estimated to be extremely low.^[7]

Muir-Torre syndrome should be considered in patients initially seen with sebaceous tumors of the eyelid or other sebaceous adenomas. Immunohistochemistry for MSH2 is a practical initial approach to screen for Muir-Torre syndrome in patients with sebaceous tumors.^[8]

The following laboratory tests can be of diagnostic value if patients present with cutaneous signs of Muir-Torre syndrome:^[9][8]

• Sigmoidoscopy may be performed for screening of colonic polyposis and colonic carcinoma.
• Endoscopy may be performed to check for an occult gastric carcinoma.
• Serum carcinoembryonic antigen values are frequently increased in patients with colonic carcinomas.
• A complete blood cell count assists in detecting hematologic malignancies.
• A bone marrow examination may be needed to further delineate a hematologic malignancy.
• Laryngoscopy with biopsy examination of any suspicious lesions can rule out an occult laryngeal carcinoma.
• Abdominal CT scanning and MRI assist in detecting an occult internal malignancy, such as kidney and urothelial cancers, in patients with Muir-Torre syndrome.
• A biopsy of skin tumors performed for histopathologic examination provides an accurate diagnosis of sebaceous neoplasms, including sebaceous adenomas.
• Histopathologic examination of specimens obtained from polypectomy (removal of individual polyps) and laryngoscopy of patients with suspected Muir-Torre syndrome confirms the presence or the absence of occult internal malignancy.
• Peripheral blood smear, bone marrow examination, and lymph node biopsy may assist in detecting an associated hematologic malignancy in these patients.

About 60% of people with MTS develop metastatic disease.  Prognosis may depend on the associated internal cancer(s) each affected person has. People with MTS should have regular screening examinations, particularly of the gastrointestinal and genitourinary tracts.^[9]