Survival Outcomes in the Canadian Merkel Cell Carcinoma Population Between 2000 and 2018 and Descriptive Comparison with the American Joint Committee on Cancer 8th Edition Staging System-A Study from the Pan-Canadian Merkel Cell Collaborative

Abstract

Background/Objectives: Merkel cell carcinoma (MCC) is an uncommon but aggressive skin malignancy with a rising incidence. Limited data exist on the survival of MCC patients in Canada. This study analyzes the survival of patients diagnosed with MCC in Canada between 2000 and 2018 compared to those reported by the American Joint Committee on Cancer (AJCC) 8th edition. Risk factors included in the database were sex, age, and immunosuppression. Methods: We conducted a multicenter retrospective cohort study including patients diagnosed with stage I-IV MCC aged ≥18 from 10 Canadian university centers and three provinces. We evaluated differences in survival compared to the cohort included in the AJCC 8th edition. Results: Among 899 patients diagnosed with MCC in Canada, 327 (36.4%) had stage I, 195 (21.7%) had stage II, 305 (33.9%) had stage III, and 72 (8.0%) had stage IV at presentation. When examining risk factors, 61.1% (549) were male, 10.2% (92) were immunosuppressed, and age at diagnosis was 75 years (±11). The five-year overall survival for patients diagnosed in Canada at stage I was 56.8%, stage IIA 54.0%, stage IIB 28.0%, stage IIIA 52.7%, stage IIIB 40.2%, and stage IV 13.9%. Conclusions: Survival from MCC is low in Canada across all stages. Compared to the AJCC 8th edition, patients diagnosed with MCC in Canada have similar survival rates, except for patients diagnosed with stage IIIB, who have lower survival rates in the AJCC 8th edition. Further research is needed to improve the survival of this rare malignancy.

Keywords: Canada; Merkel cell carcinoma; cohort study; epidemiology; treatment.

Figure 1

Five-year overall survival (OS) of Canadian Merkel cell carcinoma (MCC) patients presenting with local disease only stratified by primary tumor size using T categories (T1: primary tumor ≤ 2 cm, T2/3: primary tumor > 2 cm, T4: primary tumor invades fascia, muscle, cartilage, or bone).

Figure 2

Five-year overall survival (OS) of Canadian Merkel cell carcinoma (MCC) patients presenting with nodal metastases stratified by occult nodal disease (N1a), clinically detected nodal disease with known primary tumor (N1b with known primary), clinically detected nodal disease with unknown primary tumor (N1b with unknown primary), and in-transit metastasis (N2/3).

Figure 3

Five-year overall survival (OS) of Canadian Merkel cell carcinoma (MCC) patients stratified by American Joint Committee on Cancer (AJCC) 8th edition pathological substage including stage I (T1 N0 M0), stage IIA (T2/3 N0 M0), stage IIB (T4 N0 M0), stage IIIA (T1–4 N1a M0 and T0 N1b M0), stage IIIB (T1–4 N1b M0 and T0–4 N2 M0), and stage IV (T any Nany M1).