One hundred and eighteen studies were included in the review; 106 were non-comparative studies and 12 were single case reports. Just over half the studies (56%) were considered intermediate quality, 13% were poor quality, and 30% high quality. Follow-up duration ranged from four weeks up to 20 years (where reported).
Surgical excision: The pooled local recurrence rate after surgical excision was 5.4% (95% CI 2.5 to 9.1; 12 studies), but there was evidence of significant heterogeneity (I²=81%). Local recurrence rates were highest in the ear region after surgical excision (14.1%, 95% CI 10.2 to 18.5; three studies; I²=0%). The pooled average number of deaths attributable to disease after surgical excision was 4.1% (95% CI 1.7 to 7.6; eight studies; I²=58%).
Mohs micrographic surgery: The pooled cure rate at five years was 97.4% (95% CI 96.2 to 98.3; 16 studies; I²=48%). The pooled average local recurrence rate after Mohs micrographic surgery was 3.0% (95% CI 2.2% to 3.9%; 10 studies; I²=0%), and recurrence in regional lymph nodes was 4.2% (95% CI 2.3 to 6.6; six studies; I²=56%). The pooled average number of deaths attributable to disease was 1.1% (95% CI 0.2 to 2.6; four studies; I²=49%).
External radiotherapy: The pooled local recurrence rate after external radiotherapy was 6.4% (95% CI 3.0 to 11.0; seven studies; I²=76%). Regional lymph node failure was 2.6% (95% CI 0.04 to 8.9; three studies; I²=70%). The pooled average number of deaths attributable to disease was 9.1% (95% 1.4 to 22.8; five studies; I²=79%).
Brachytherapy: The average local recurrence rate after brachytherapy was 5.2% (95% CI 1.6 to 10.5; six studies; I²=0%). None of the studies reported on deaths attributable to disease.
Radiotherapy plus surgery: The average local recurrence rate after treatment for perineural invasion was 18.2% (95% CI 3.8 to 39.8; five studies; I²=37%) and for other types of carcinoma was 11.1% (95% CI 2.4 to 25.0; four studies; I²=35%). The average number of deaths due to disease was 11.1% (95% CI 0.4 to 33.1; I²=45%) for perineural invasion, and 13.9% (95% CI 0.05 to 50.2; I²=74%) for other types of carcinoma.
Curettage and electrodesiccation: Recurrence (not specified) after curettage and electrodesiccation was 1.7% (95% CI 0.6 to 3.4; eight studies; I²=59%).
Cryotherapy: The average recurrence of disease after cryotherapy was 0.8% (95% CI 0.1 to 2.2; eight studies; I²=0%).
Photodynamic therapy: The average proportion of participants having complete response to treatment was 72.0% (95% CI 66.9 to 76.8% - figures taken from forest plot; 18 study arms; I²=71%) using a fixed-effect model. The pooled recurrence rate in participants who had completely responded initially to photodynamic therapy was 26.0% (95% CI 12.0 to 44.0 - figures taken from forest plot; 10 study arms; I²=72%).
Other findings (including distant and unspecified recurrence rates) and findings from subgroup and sensitivity analyses were reported in the review.