Effect of radiotherapy dose and volume on relapse in Merkel cell cancer of the skin.
OBJECTIVE
To assess the effect of radiotherapy (RT) dose and volume on relapse patterns in patients with Stage I-III Merkel cell carcinoma (MCC).


METHODS
This was a retrospective analysis of 112 patients diagnosed with MCC between January 2000 and December 2005 and treated with curative-intent RT.


RESULTS
Of the 112 evaluable patients, 88% had RT to the site of primary disease for gross (11%) or subclinical (78%) disease. Eighty-nine percent of patients had RT to the regional lymph nodes; in most cases (71%) this was for subclinical disease in the adjuvant or elective setting, whereas 21 patients (19%) were treated with RT to gross nodal disease. With a median follow-up of 3.7 years, the 2-year and 5-year overall survival rates were 72% and 53%, respectively, and the 2-year locoregional control rate was 75%. The in-field relapse rate was 3% for primary disease, and relapse was significantly lower for patients receiving >or=50 Gy (hazard ratio [HR] = 0.22; 95% confidence interval [CI], 0.06-0.86). Surgical margins did not affect the local relapse rate. The in-field relapse rate was 11% for RT to the nodes, with dose being significant for nodal gross disease (HR = 0.24; 95% CI, 0.07-0.87). Patients who did not receive elective nodal RT had a much higher rate of nodal relapse compared with those who did (HR = 6.03; 95% CI, 1.34-27.10).


CONCLUSIONS
This study indicates a dose-response for subclinical and gross MCC. Doses of >or=50 Gy for subclinical disease and >or=55 Gy for gross disease should be considered. The draining nodal basin should be treated in all patients.
Foote
Matthew
M
Division of Cancer Services, Princess Alexandra Hospital, University of Queensland, Brisbane, Queensland, Australia. matthew_foote@health.qld.gov.au
Harvey
Jennifer
J
Porceddu
Sandro
S
Dickie
Graeme
G
Hewitt
Susan
S
Colquist
Shoni
S
Zarate
Dannie
D
Poulsen
Michael
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015266:Carcinoma, Merkel Cell / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D016001:Confidence Intervals; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D015182:Lymphatic Irradiation; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000401:mortality; D012189:Retrospective Studies; D012878:Skin Neoplasms / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D015996:Survival Rate