This article needs attention from an expert in medicine. The specific problem is: Unsure about recent edits.(December 2020) |
Merkel cell carcinoma | |
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Micrograph of a Merkel cell carcinoma. H&E stain. | |
Specialty | Oncology |
Merkel cell carcinoma (MCC) is a rare and aggressive skin cancer occurring in about three people per million members of the population. [1] It is also known as cutaneous APUDoma, primary neuroendocrine carcinoma of the skin, primary small cell carcinoma of the skin, and trabecular carcinoma of the skin. [2] Factors involved in the development of MCC include the Merkel cell polyomavirus (MCPyV or MCV), a weakened immune system, and exposure to ultraviolet radiation. [3] Merkel cell carcinoma usually arises on the head, neck, and extremities, as well as in the perianal region and on the eyelid. [4] It is more common in people over sixty years old, Caucasian people, and males. [5] MCC is less common in children. [1] [4]
Merkel cell carcinoma (MCC) usually presents as a firm nodule (up to 2 cm diameter) or mass (>2 cm diameter). These flesh-colored, red, or blue tumors typically vary in size from 0.5 cm (less than one-quarter of an inch) to more than 5 cm (2 inches) in diameter and may enlarge rapidly. Tumors can present as painless, tender or itchy, and other MCC manifestations as papules or plaques have also been reported. [6] Although MCC may arise almost anywhere on the body, it is most commonly found in sun-exposed areas such as the head, neck or extremities. [7] Five key attributes of MCC were summarized in 2008 in the acronym AEIOU (Asymptomatic/lack of tenderness, Expanding rapidly, Immune suppression, Older than 50 years, and Ultraviolet-exposed site on a person with fair skin). [8] Ninety percent of MCC's have three or more of those features. [9] MCC is sometimes mistaken for other histological types of cancer, including basal cell carcinoma, squamous cell carcinoma, malignant melanoma, lymphoma, and small cell carcinoma, or as a benign cyst. [10] Merkel cell carcinomas have been described in children, but pediatric cases are very rare. [11]
Merkel cell cancers tend to invade locally, infiltrating the underlying subcutaneous fat, fascia, and muscle, and typically metastasize early in their natural history, most often to the regional lymph nodes. MCCs also spread aggressively through the blood vessels to many organs, particularly to liver, lung, brain, and bone. [12]
Although MCC was initially named for the Merkel cell due to histologic and physiologic similarities between MCC and Merkel cells, the cellular progenitor of MCC has been a heavily debated question. Merkel cells are highly specialized cells that act as pressure receptors in the epidermis. The origin of Merkel cells themselves is debated and proposed to be derived from neural crest cells or epidermal progenitors. [14] MCC is similar to Merkel cells in its histological appearance (see below: Diagnosis) and shares many immunohistochemical markers with Merkel cells, including epidermal marker cytokeratin 20 and neuroendocrine markers synaptophysin and chromogranin A. Furthermore, the ion channel Piezo2 and transcription factor Atoh1, both specific to Merkel cells, are also expressed by MCC. [3] However, Merkel cells are post-mitotic cells with a low probability of cancerous transformation. [14] Additionally, they have not been shown to support Merkel cell polyoma virus infection, which is believed to drive oncogenesis in approximately 80% of MCC. [15]
Instead, it has been proposed the MCC may originate from a Merkel cell precursor, at which point it gains features similar to those of Merkel cells. One such precursor is the human fibroblast. Evidence for a fibroblast precursor includes its location in the dermis, which is thought to be the primary site of origin for MCC. Additionally, in vitro experiments have demonstrated that fibroblasts not only support Merkel cell polyomavirus (MCV) infection but can be induced into having a MCC phenotype by the expression of viral proteins. [15] [16]
However, others have argued that MCC likely derives from an epithelial precursor cell due to its frequent presence in mixed tumors including epithelial neoplasms such as squamous cell carcinoma. While epithelial cells are not typically found in the dermis, hair follicles include epithelial cells that have been shown to have oncogenic potential, and have therefore been proposed as a possible site for a MCC precursor. [3] [17]
Finally, the presence of B-cell surface markers on MCC in addition to the high correlation between MCC and B-cell lymphomatous cancers have also led to suggestions that MCC may share a progenitor with B-cells. [3] [18] Because of the differences in physiology and prognosis between MCV+ and MCV- MCC (see below), however, some have suggested that these two subtypes of MCC may actually derive from different progenitor cells. [19]
Several factors are involved in the pathophysiology of MCC, including MCV, ultraviolet radiation (UV) exposure, and weakened immune function. [20]
The MCV is a small double-stranded DNA virus that is believed to contribute to the development of the majority of MCC. [21] About 80% of MCC tumors are infected with MCV, with the virus integrated into the host genome in a monoclonal pattern. [21] However, the majority of people with MCV infection do not develop MCC: MCV is a ubiquitous virus and infection commonly occurs during childhood but remains asymptomatic throughout an individual's lifetime. [16]
MCC was first believed to be associated with MCV when it was observed to occur at a much higher rate in HIV patients during the 1980s. [22] Since then, studies have demonstrated integration of the MCV genome into the genome of MCC tumor cells. Central to the understanding of the pathogenicity of MCV are two viral proteins expressed in infected cells known as the large tumor antigen (LT) and small tumor antigen (sT). [23] Normally, patients infected with MCV show low levels of antibodies to the LT protein, perhaps due to a nuclear localization domain in its C-terminal that limits its cellular dispersion. However, integration of the viral genome into the host genome can result in truncation of the LT protein proximal to this domain. This serves two oncogenic purposes: first, it prevents successful viral replication that would culminate in lysis of the infected cell. Second, it redistributes the LT protein to the cytoplasm, where it can interact with cytoplasmic signaling. [24] The N-terminal LXCXE motif of the LT protein has been shown to interact with known oncogene Rb and is conserved in other cancer-causing viruses. [24] Studies suggest that LT may also preserve cell proliferation signals such as c-Myc and cyclin E and cause DNA injury to the p53 tumor suppressor. [15] [16]
Meanwhile, sT has been shown to induce cell proliferation through hyper-phosphorylation of the translation initiator 4EBP1 as well as inhibition of a ubiquitin ligase complex responsible for degradation of cellular proliferation signals. sT also contains a region known as the LT stabilization domain (LSD), which potentiates the LT protein's oncogenic function. Unlike LT, MCC samples have been identified that express sT alone, and sT expression in fibroblasts has been shown to cause MCC phenotype development. [15] [16]
About 20% of MCC tumors are MCV negative. [7] In contrast to MCV-induced MCC, these tumors tend to have much higher mutational burdens with mutational signatures characteristic of UV damage. [15] Genes frequently mutated in MCV-negative MCC include p53 and Rb, among others. [23] The link between MCC and UV exposure has been demonstrated through various epidemiological studies indicating a higher incidence of MCC in fair-skinned people in areas of high UV exposure, as well as among those receiving UV phototherapy. [6] The typical distribution of MCC in sun-exposed regions and its co-occurrence with other skin cancers also indicate that UV exposure is a contributing factor to MCC development. It is unclear whether this is through direct mutational impact, immune down-regulation, or some combination of the two. [6] [10]
The incidence of MCC is increased in conditions with defective immune functions such as malignancy, HIV infection, and organ transplant patients, etc. [6] Conversely, patients with brisk immune response have been shown to have improved prognoses. [25] This is suspected to be due to the inability of the body to defend itself from infection by or reactivation of MVC. [26] The body of data indicating the importance of immune function in MCC pathogenesis has been exploited for the development of immunotherapies discussed below.
Diagnosis of MCC begins with a clinical examination of the skin and lymph nodes to determine suspicious areas for further investigation. [28] Definitive diagnosis requires examination of biopsy tissue to identify its histopathologic features. [6] [28] An ideal biopsy specimen is either a punch biopsy or a full-thickness incisional biopsy of the skin including full-thickness dermis and subcutaneous fat. On light microscopy, MCC shows basaloid tumor nests with neuroendocrine features ("salt and pepper" chromatin, scarce cytoplasm, and brisk mitotic activity). [6] [28] In addition to standard examination under light microscopy, immunohistochemistry (IHC) is also generally required to differentiate MCC from other morphologically similar tumors such as skin metastases of small cell lung cancer, the small cell variant of melanoma, various cutaneous leukemic/lymphoid neoplasms, and Ewing's sarcoma. Neuroendocrine molecular markers such as synaptophysin or chromogranin A are characteristic of MCC and other neuroendocrine tumors, while other markers such as PAX5 or cytokeratin 20 can distinguish MCC from these tumors. [3] [7] Longitudinal imaging may also help in ruling out a diagnosis of metastatic small cell lung cancer. Once an MCC diagnosis is made, a sentinel lymph node biopsy as well as imaging are recommended as a part of the staging process, which determines prognosis and subsequent treatment options. [6] [28] Imaging may include positron emission tomography or CT scan. [29]
Sunlight exposure is thought to be one of the causes of Merkel cell carcinoma (MCC). The World Health Organization, American Academy of Dermatology, and Skin Cancer Foundation recommend the following measures to prevent excessive UV exposure and skin cancer: [30] [31] [32]
This section needs more reliable medical references for verification or relies too heavily on primary sources .(March 2017) |
Merkel cell carcinoma is typically treated with surgery and radiation; immunotherapy is used in advanced disease. If an affected person is being treated with immunosuppressive drugs, they are reduced as much as possible. [29]
Surgical resection is typically performed prior to other treatments, if possible. The type of surgery used may be a simple wide excision or a more specialized technique like Mohs surgery, depending on the individual. Part of the staging process – sentinel lymph node biopsy – is often performed at the same time. [29]
Radiation therapy is the primary management of Merkel cell carcinoma (MCC). The largest studies to date, from Australia, demonstrated that radiotherapy alone achieves equal outcomes with upfront or neoadjuvant surgery followed by radiation therapy. [33] [34] The role of surgery is largely historical and relegated to biopsy. There have been no head-to-head trials comparing the two treatment strategies, and in the absence of this, surgeons tend to most commonly perform excisional biopsy prior to referring for radiation therapy to eradicate MCC. MCC is exquisitely radiosensitive. [35] The conclusion amongst published studies in the Radiation Oncology community is that MCC should be managed ideally with radiation therapy alone. [34]
Because of its significant adverse effects, traditional chemotherapy has been saved for late-stage highly metastasized cases of MCC. While some chemotherapeutic regimens have been shown to have transient effects, studies have not found any significant long-term effect on recurrence rate or life expectancy. [15] As of 2015, there were no FDA-approved standard chemotherapy regimens for MCC treatment. [25] The most recent American guidelines do not recommend adjuvant chemotherapy, citing a lack of evidence to suggest improved outcomes. Instead, consideration of the need for chemotherapy on a case-by-case basis is recommended. [36]
Immunotherapies, namely inhibitors of the PD1-PDL1 checkpoint signaling pathway, are novel anticancer agents that have shown benefit in advanced-stage MCC or chemotherapy-resistant MCC. [37] The PD-1 pathway is responsible for regulating the balance between T-cell activation and over-activation leading to T-cell exhaustion or autoimmunity. [38] However, over-expression of PD-1 ligands (PDL1) have been observed in tumors as a method of evading immune attack. [39] PD-1 inhibition therefore enhances the body's immune response, enabling it to target cancer cells for destruction. [40] Due to their side effects, however, National Comprehensive Cancer Network guidelines recommend PD-1 inhibitors for people with disseminated rather than early-stage MCC. [9]
PD1/PDL1 pathway inhibitors approved or in clinical trials for use in MCC treatment include:
Studies to date have shown a clinical response rate between 50 and 65% for MCC treated with PD-1 pathway inhibitors. Suggestions for further immunotherapy research areas have included therapeutic vaccines or epigenetic modification of HLA-receptors. [23] [24] [25] [37]
According to the American Joint Committee on Cancer (AJCC), the natural course of MCC is "variable and depends heavily on the stage at diagnosis". [45] Staging of MCC is classified according to the TNM staging system, a notation system that describes the stage of cancer according to the size of the primary tumor (T), the degree of spread to regional lymph nodes (N), and the presence of distant metastasis (M). [45] A combination of T, N, and M stages dictate the final clinical stage group (0, I, IIA, IIB, IIIA, IIIB, IV). [46] Advanced stage (i.e. increased size of the tumor, spreading of the tumor into surrounding and/or distant tissue, and involvement of lymph nodes) is associated with lower survival rates. [7]
The National Cancer Data Base has survival rates collected from nearly 3000 MCC patients from year 1996–2000 with 5-year survival rates listed as follows: [47] Stage IA: 80%. Stage IB: 60%. Stage IIA: 60%. Stage IIB: 50%. Stage IIC: 50%. Stage IIIA: 45%. Stage IIIB: 25%. Stage IV: 20%. Five-year survival may be 51% among people with localized disease, 35% for those with nodal disease, and 14% with metastases to a distant site. [9]
Several other features may also affect prognosis, independent of tumor stage. They include MCV viral status, histological features, and immune status. In viral status, MCV large tumor antigen (LT antigen) and retinoblastoma protein (RB protein) expression correlates with more favorable prognosis, while p63 expression correlates with a poorer prognosis. [48] [49] Histological features such as intratumoral CD8+ T lymphocyte infiltration may be associated with a favorable prognosis, while lymphovascular infiltrative pattern may be associated with a poorer prognosis. [50] [51] Immunosuppressed status, especially T cell immunosuppression (e.g., organ transplant, HIV infection, certain malignancy) predicts poorer prognosis and higher mortality. [52] Immunosuppression also raises the risk of recurrence. [29]
The antibody titer in the blood to the Merkel cell polyomavirus oncoprotein can be used as a treatment response biomarker in people that have detectable antibodies at the time of diagnosis. [53] [54]
Merkel cell carcinoma occurs most often in Caucasians between 60 and 80 years of age. Its incidence is about twice as high in males as in females. [55] It is a rare type of skin cancer, with a 2013 incidence of only 0.7 per 100,000 persons in the U.S. [56] As of 2005, roughly 2,500 new cases of MCC are diagnosed each year in the United States, [56] as compared to around 60,000 new cases of malignant melanoma and over 1 million new cases of nonmelanoma skin cancer. [57] Similar to melanoma, the incidence of MCC in the US is increasing rapidly. [10] Worldwide, MCC is most commonly found in regions with increased sun exposure. Australia is the country with the highest incidence of MCC [55] but has a lower incidence of MCV-positive MCC than observed in other countries. [58]
Since 2006, it has been known that other primary cancers increase the risk of MCC significantly, especially in those with the prior multiple myeloma, chronic lymphocytic leukemia, and malignant melanoma. [59] Immunosuppression including HIV infection or immunosuppressant therapy following organ transplant or for autoimmune disease can also increase the odds of developing MCC. [20]
Friedrich Sigmund Merkel (1845–1919) was a German anatomist and histopathologist who first described the Tastzellen (touch cells) in the skin in 1875. [60] In 1878 the term Merkel cell was coined by the anatomist Robert Bonnet (1851–1921).
Merkel cell carcinoma was first described in 1972 by Cyril Toker. [61] He reported five cases of 'trabecular carcinoma of the skin'.
Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. It occurs when skin cells grow uncontrollably, forming malignant tumors. The primary cause of skin cancer is prolonged exposure to ultraviolet (UV) radiation from the sun or tanning devices. Skin cancer is the most commonly diagnosed form of cancer in humans. There are three main types of skin cancers: basal-cell skin cancer (BCC), squamous-cell skin cancer (SCC) and melanoma. The first two, along with a number of less common skin cancers, are known as nonmelanoma skin cancer (NMSC). Basal-cell cancer grows slowly and can damage the tissue around it but is unlikely to spread to distant areas or result in death. It often appears as a painless raised area of skin that may be shiny with small blood vessels running over it or may present as a raised area with an ulcer. Squamous-cell skin cancer is more likely to spread. It usually presents as a hard lump with a scaly top but may also form an ulcer. Melanomas are the most aggressive. Signs include a mole that has changed in size, shape, color, has irregular edges, has more than one color, is itchy or bleeds.
Cutaneous squamous-cell carcinoma (cSCC), also known as squamous-cell carcinoma of the skin or squamous-cell skin cancer, is one of the three principal types of skin cancer, alongside basal-cell carcinoma and melanoma. cSCC typically presents as a hard lump with a scaly surface, though it may also present as an ulcer. Onset and development often occurs over several months. Compared to basal cell carcinoma, cSCC is more likely to spread to distant areas. When confined to the epidermis, the outermost layer of the skin, the pre-invasive or in situ form of cSCC is termed Bowen's disease.
Basal-cell carcinoma (BCC), also known as basal-cell cancer, basalioma or rodent ulcer, is the most common type of skin cancer. It often appears as a painless raised area of skin, which may be shiny with small blood vessels running over it. It may also present as a raised area with ulceration. Basal-cell cancer grows slowly and can damage the tissue around it, but it is unlikely to spread to distant areas or result in death.
Melanoma is the most dangerous type of skin cancer; it develops from the melanin-producing cells known as melanocytes. It typically occurs in the skin, but may rarely occur in the mouth, intestines, or eye. In women, melanomas most commonly occur on the legs; while in men, on the back. Melanoma is frequently referred to as malignant melanoma. However, the medical community stresses that there is no such thing as a 'benign melanoma' and recommends that the term 'malignant melanoma' should be avoided as redundant.
Head and neck cancer is a general term encompassing multiple cancers that can develop in the head and neck region. These include cancers of the mouth, tongue, gums and lips, voice box (laryngeal), throat, salivary glands, nose and sinuses. Head and neck cancer can present a wide range of symptoms depending on where the cancer developed. These can include an ulcer in the mouth that does not heal, changes in the voice, difficulty swallowing, red or white patches in the mouth, and a neck lump.
Polyomaviridae is a family of viruses whose natural hosts are primarily mammals and birds. As of 2024, there are eight recognized genera. 14 species are known to infect humans, while others, such as Simian Virus 40, have been identified in humans to a lesser extent. Most of these viruses are very common and typically asymptomatic in most human populations studied. BK virus is associated with nephropathy in renal transplant and non-renal solid organ transplant patients, JC virus with progressive multifocal leukoencephalopathy, and Merkel cell virus with Merkel cell cancer.
Mycosis fungoides, also known as Alibert-Bazin syndrome or granuloma fungoides, is the most common form of cutaneous T-cell lymphoma. It generally affects the skin, but may progress internally over time. Symptoms include rash, tumors, skin lesions, and itchy skin.
Cancer immunotherapy (immuno-oncotherapy) is the stimulation of the immune system to treat cancer, improving the immune system's natural ability to fight the disease. It is an application of the fundamental research of cancer immunology (immuno-oncology) and a growing subspecialty of oncology.
Invasive carcinoma of no special type, invasive breast carcinoma of no special type (IBC-NST), invasive ductal carcinoma (IDC), infiltrating ductal carcinoma (IDC) or invasive ductal carcinoma, not otherwise specified (NOS) is a disease. For international audiences this article will use "invasive carcinoma NST" because it is the preferred term of the World Health Organization (WHO).
Patrick S. Moore is an American virologist and epidemiologist who co-discovered together with his wife, Yuan Chang, two different human viruses causing the AIDS-related cancer Kaposi's sarcoma and the skin cancer Merkel cell carcinoma. Moore and Chang have discovered two of the seven known human viruses causing cancer. The couple met while in medical school together and were married in 1989 while they pursued fellowships at different universities.
Vulvar cancer is a cancer of the vulva, the outer portion of the female genitals. It most commonly affects the labia majora. Less often, the labia minora, clitoris, or Bartholin's glands are affected. Symptoms include a lump, itchiness, changes in the skin, or bleeding from the vulva.
Transitional cell carcinoma is a type of cancer that arises from the transitional epithelium, a tissue lining the inner surface of these hollow organs. It typically occurs in the urothelium of the urinary system; in that case, it is also called urothelial carcinoma. It is the most common type of bladder cancer and cancer of the ureter, urethra, and urachus. Symptoms of urothelial carcinoma in the bladder include hematuria. Diagnosis includes urine analysis and imaging of the urinary tract (cystoscopy).
A paraneoplastic syndrome is a syndrome that is the consequence of a tumor in the body. It is specifically due to the production of chemical signaling molecules by tumor cells or by an immune response against the tumor. Unlike a mass effect, it is not due to the local presence of cancer cells.
Thymic carcinoma, or type C thymoma, is a malignancy of the thymus. It is a rare cancer that is often diagnosed at advanced stages. Recurrence following treatment is common, and thymic carcinoma is associated with a poor prognosis.
Merkel cell polyomavirus was first described in January 2008 in Pittsburgh, Pennsylvania. It was the first example of a human viral pathogen discovered using unbiased metagenomic next-generation sequencing with a technique called digital transcriptome subtraction. MCV is one of seven currently known human oncoviruses. It is suspected to cause the majority of cases of Merkel cell carcinoma, a rare but aggressive form of skin cancer. Approximately 80% of Merkel cell carcinoma (MCC) tumors have been found to be infected with MCV. MCV appears to be a common—if not universal—infection of older children and adults. It is found in respiratory secretions, suggesting that it might be transmitted via a respiratory route. However, it has also been found elsewhere, such as in shedded healthy skin and gastrointestinal tract tissues, thus its precise mode of transmission remains unknown. In addition, recent studies suggest that this virus may latently infect the human sera and peripheral blood mononuclear cells.
Trichodysplasia spinulosa polyomavirus is a member virus of Human polyomavirus 8 that infects human hosts. First discovered in 2010, TSPyV is associated with Trichodysplasia spinulosa, a rare skin disease only seen in immunocompromised patients. The virus causes hyperproliferation and enlargement of hair follicles by modulating PP2A protein phosphatase signaling pathways. TSPyV was the eighth human polyomavirus to be discovered, and one of four associated with human disease, out of 13 human polyomaviruses known as of the 2015 update to polyomavirus taxonomy released by the International Committee on Taxonomy of Viruses.
Wolfram Samlowski is an American medical oncologist with Comprehensive Cancer Centers of Nevada (CCCN) and a member of the Research Developmental Therapeutics and Genitourinary Committees for US Oncology. His research interests include translational research and development of novel cancer immunotherapy agents, translational drug development as well as gene therapy. His clinical interests are in developing more effective treatments for advanced stages of melanoma and non-melanoma skin cancers, and renal cancer.
Avelumab, sold under the brand name Bavencio, is a fully human monoclonal antibody medication for the treatment of Merkel cell carcinoma, urothelial carcinoma, and renal cell carcinoma.
PD-1 inhibitors and PD-L1 inhibitors are a group of checkpoint inhibitor anticancer drugs that block the activity of PD-1 and PDL1 immune checkpoint proteins present on the surface of cells. Immune checkpoint inhibitors are emerging as a front-line treatment for several types of cancer.
Squamous-cell carcinoma (SCC), also known as epidermoid carcinoma, comprises a number of different types of cancer that begin in squamous cells. These cells form on the surface of the skin, on the lining of hollow organs in the body, and on the lining of the respiratory and digestive tracts.
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