Cholecystectomy and the risk of alimentary tract cancers: A systematic review

Table 6 Descriptive characteristics of studies on the association between cholecystectomy and extrahepatic bile duct cancer

Ref.	Period of study	Study design	No. of cases	No. of controls	Exposure ascertainment	Outcome ascertainment	Follow-up (yr)	Effect estimate	Adjustments	Quality of publication
Nogueira et al[21], 2014	1992-2005	Case-control	118/3681	2572/100000	Medicare database	Cancer registry	> 6	OR = 1.19 (0.98-1.43)	Age, gender, diabetes	49
Chow et al[34], 1999	1977-1993	Cohort	16/42461	NA	National registry	Cancer registry	≥ 4	0.7 (0.3-1.4)	Age, gender, obesity, years of follow-up, other comorbidities	33
Chen et al[29], 2014	2000-2010	Cohort	9/5850		National database	Cancer registry	10	2.22 (0.91-5.41)	Age, gender, comorbidities	53

NA: Not available.