Prognosis

MCC is an aggressive cutaneous tumor with a risk of locoregional and distant metastases. Prognosis depends on several factors, including increasing primary tumor size and advancing stage of disease.

Reported 5-year overall survival rates vary widely, ranging from:[1][7][10][19]​​[31][32]​​[33][34][35][36][37][38][81][82][83]​​​[84]​​​​[85]​​​​​​​​​​​​​​​​​[86]

  • 51% to 73% for local disease

  • 35% to 63% for nodal disease

  • 14% to 29% for distant disease.

MCC-specific survival is higher than overall survival. Based upon a Seattle-based data repository between 2003 and 2019, 5-year MCC-specific survival rates were 95% for stage I, 80% for stage III, 78% for stage IIIA, 56% for stage IIIB, and 41% for stage IV.[79]​ One UK study found an overall 5-year net survival estimate for MCC diagnosed at any stage of 49.4% based on 2013 diagnosis (95% CI 40.2 to 58.7), with case numbers too small to provide net survival estimates according to stage.[87]

Other than stage at diagnosis, clinical factors associated with a poorer prognosis include older age, male sex, head/neck primary site, primary tumor size >2 cm, and the presence of immunosuppression.​[7][18][19][27][77]​​​ One study found that Hispanic ethnicity was associated with improved survival compared with white patients and that black patients had similar MCC-specific survival to white patients despite presenting with more advanced disease.[41] The authors postulated that these findings could be attributable to a higher proportion of cases being Merkel cell polyomavirus (MCPyV)-positive in darker-skinned individuals.

Patients who present with unknown primary MCC (i.e., nodal or distant metastases without a primary lesion) have significantly better survival rates than those who have similar extent of disease but with a known primary lesion.[29]​​[35][46][47]​​ This group was downstaged in the AJCC8 MCC staging system to IIIA, as their prognosis aligns with the prognosis for patients presenting with a primary tumor and occult lymph node metastasis.[10]

Following treatment, patients are at risk of local, regional, and/or distant recurrence. There is a high risk of recurrence in the first year, and 95% of recurrences happen within the first 3 years of diagnosis.[79]​ Patients whose tumors are MCPyV-negative may have a higher risk of recurrence than those whose tumors test MCPyV-positive.[3] An estimate of recurrence risk based on initial stage, time to treatment, and other risk factors such as age, sex, immunosuppression, and location of primary tumor can be calculated at: Merkelcell.org: recurrence risk calculator Opens in new window[79][80]​​​

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