Embase	#1 ‘basal cell carcinoma’/exp OR ‘basal cell carcinoma’
	#2 ‘perianal’ OR ‘anus’
	#3 ‘epithelioma’
	#4 ‘basal cell’
	#5 #1 AND #2
	#6 #2 AND #3 AND #4
	#7 #5 OR #6
Medline (Clarivate Analytics)	(basal cell) AND (carcinoma or epithelioma) AND (perianal or anus or anal)
PubMed	#1 ‘basal cell carcinoma’
	#2 ‘perianal’ OR ‘anus’
	#3 ‘epithelioma’
	#4 ‘basal cell’
	#5 #1 AND #2
	#6 #2 AND #3 AND #4
	#7 #5 OR #6