Table 1.

Summary of the 55 studies included in the systematic review

	Year of study	Country	Study type	First occurrence	Study quality a
Villet WT et al. 16	1977	South Africa	Case report	CLL first	1
Weimar VM et al. 17	1979	USA	Case series	CLL first and simultaneous CLL and cSCC	1
Mora, RG 28	1985	USA	Case report	CLL first	1
Bridges N et al. 39	1986	USA	Case report	CLL first	1
Lishner M et al. 50	1987	Israel	Case series	CLL first	2
Perez‐Reyes N, Farhi DC. 61	1987	USA	Retrospective cohort study	CLL first	2
Frierson HF et al. 66	1988	USA	Retrospective cohort study	CLL first	2
Soares FA et al. 67	1992	Brazil	Case report	Simultaneous CLL and cSCC	1
Adami J et al. 68	1995	Sweden, Denmark	Retrospective cohort study	CLL first and cSCC first	2
Hartley BEJ et al. 69	1996	UK	Case series	CLL first and cSCC first	1
Levi F et al. 18	1996	Switzerland	Retrospective cohort study	CLL first and cSCC first	2
Davidovitz Y et al. 19	1997	Israel	Case report	CLL first	1
Dargent JL et al. 20	1998	Belgium	Case report	CLL first	1
Albregts T et al. 21	1998	USA	Case report	CLL first	1
Smoller BR et al. 22	1998	USA	Case series	CLL first	1
Gray Y et al. 23	2001	USA	Case report	CLL first	1
Smith KJ et al. 70	2001	USA	Case series	Simultaneous CLL and cSCC	1
Pigeaud‐Klessens ML et al. 24	2002	Netherland	Case report	CLL first	1
Larsen CR et al. 25	2002	Denmark	Case series	CLL first	1
Padgett JK et al. 26	2003	USA	Case report	cSCC first	1
Agnew KL et al. 27	2004	UK	Retrospective cohort study	CLL first	2
Rashid K et al. 29	2005	USA	Case series	CLL first	1
Sheahan P et al. 30	2005	Ireland	Retrospective cohort study	SCC first	2
Mehrany K et al. 31	2005	USA	Retrospective case–control study	Simultaneous CLL and cSCC	2
Mehrany K et al. 32	2005	USA	Retrospective case–control study	Simultaneous CLL and cSCC	2
Flezar MS et al. 33	2006	Slovenia	Case series	CLL first	1
Goh MSY 34	2006	Australia	Case series	CLL first	1
Wong J. et al. 35	2008	Canada	Case report	CLL first	1
Peng Y et al. 36	2009	USA	Case report	CLL first	1
Toro JR et al. 37	2009	USA	Retrospective cohort study	cSCC first	3
Hodges S. et al. 38	2010	UK	Case report	Simultaneous CLL and cSCC	1
Wilson ML et al. 40	2010	USA	Case series	Simultaneous CLL and cSCC	1
Tomaszewski JM et al. 41	2014	Australia	Case series	CLL first	1
Mansfield AS et al. 42	2014	USA	Retrospective + prospective cohort study	CLL first	2
Velez NF et al. 43	2014	USA	Retrospective cohort study	CLL first	3
Brewer JD et al. 44	2014	USA	Retrospective cohort study	CLL first	3
Tomaszewski JM et al. 45	2014	Australia	Retrospective cohot study	CLL first	3
Dos Santos HT et al. 46	2015	Brazil	Case report	CLL first	1
Vyas R et al. 47	2015	USA	Case report	CLL first	1
Gaide O et al. 48	2016	Switzerland	Case report	CLL first	1
Wollina U et al. 49	2016	Germany	Case report	Simultaneous CLL and cSCC	1
Hock BD et al. 51	2016	New Zealand	Retrospective cohort study	CLL first	2
Kader I et al. 52	2016	Australia	Retrospective cohort study	CLL first	2
Penne M et al. 53	2017	USA	Retrospective cohort study	CLL first	3
Hirshoren N et al. 54	2017	Australia	Case series	cSCC first	3
Hampras S.S et al. 55	2017	USA	Retrospective cohort study	CLL first	3
Callaghan DJ et al. 56	2018	USA	Case series	cSCC first and simultaneous CLL and cSCC	1
Wee E et al. 57	2018	Australia	Retrospective cohort study	cSCC first	2
Walz JS et al. 58	2018	Germany	Retrospective cohort study	CLL first	3
Rausch CR, Kontoyiannis DP 59	2019	USA	Case report	CLL first	1
Purcell RV et al. 60	2019	New Zealand	Retrospective cohort study	CLL first	3
Zheng G et al. 62	2019	Sweden	Retrospective cohort study	CLL first and cSCC first	2
Inda JJ et al. 63	2019	USA	Retrospective cohort study	CLL first	2
Thiesen I et al. 64	2019	Germany	Retrospective cohort study	CLL first	2
Wu PA et al. 65	2019	USA	Retrospective cohort study	CLL first	2

CLL, chronic lymphocytic leukemia; cSCC, cutaneous squamous cell carcinoma; UK, United Kingdom; USA, United States of America.

^a Based on Newcastle–Ottawa scale modified for case series and case reports: 1(worse) to 4 (better).