Efficacy

There are no reported RCTs or cohort studies on the use of sunscreens and the risk for cutaneous melanoma. There are a total of 15 case-control studies26-40 (see Table 23.1). In attempting to assess the evidence from these it is important to note that these studies use very different populations and different cultural groups. This analysis does not compare like with like: each uses a different study design, has different terms of reference and uses different methods for data collection. The term sunscreen is variously described and does not refer to one category. Sun lotion, sun-tanning oil and sun protection factor are used throughout these studies. This makes it particularly difficult to assess the reported results unless these terms were clearly defined to study participants, or confounding factors accounted for, as part of the data analysis process. Overall, however, these studies showed on overall low prevalence of sunscreen use (see Table 23.1)

Klepp and Magnus (1979)26, Graham et al. (1985)27 and Herzfeld et al. (1985)28 reported an increased risk between sunscreen use and melanoma with Graham et al. reporting an increased risk particularly in males. Beitner et al. (1990)29 reported increased risk for those who used sunscreens "often" or "very often". This study controlled for age, sex and hair colouring. Elwood and Gallagher (1999)30 assessed the relationship between phenotype, history of sun-tanning and sunburn, exposure to sunlight and the risk for melanoma in four western provinces of Canada. Analysis of a subset of cases of

Table 23.1 Case-control studies of sunscreen use and risk for cutaneous melanoma

Population

Type of cases/

No. cases/

Exposure

RRa (95% CI)

Comments

Reference

place/date

controls

controls

Norway 1974-75

Hospital cases

78 cases

Sometimes,

M 2-8b (1-2-6-7)

Elevated risks

Klepp and

Other cancer

131 controls

often or almost

F 1-0b (0-42-2-5)

among males only.

Magnus

controls

always use sun

Sunscreens not

(1979)26

lotion/oil

T 2-3b (1-3-4-1)

differentiated from

"sun lotions".

USA 1974-80

Hospital cases

404 cases

Used sunscreen

M 2-2b (1-2-4-1)

Elevated risks

Graham

Other cancer

521 controls

Used suntan

M 1-7 (1-1-2-7)

among males only

et al.

controls

lotion

F "no added risk"

(1985)27

USA 1977-79

Population cases

324 male

Always used

2-6b (1-4-4-7)

"Suntan lotions"

Herzfeld

and controls

trunk melan

"suntan lotion"

Not significant after

and "sunscreens"

et al.2"

oma cases

control for "tendency

not differentiated

(1993)

415 controls

to sunburn and

in questionnaire

water sports"

Sweden 1978-83

Hospital cases

523 cases

Often used sun

1-8b (1-2-2-7)

Beitner

Population controls

505 controls

protection

et al.29

agents

(1990)

Canada 1979-81

Population cases

369 trunk and

Used sunscreen

1-1 (0-75-1-6)

Highest risk in

Elwood and

and controls

lower limb

almost always

those using sun-

Gallagher30

melanomas

screen "only for

(1999)

369 controls

first few hours"

RR,1-62 (1-04-2-52)

Australia

Population cases

507 cases

Used

1-1 (0-71-1-6)

Holman

1980-81

and controls

507 controls

sunscreens <

et al.31

10 years

(1986)

USA 1981-86

Population cases

452 cases

Always used

All cutaneous

Study involved

Holly

and controls

930 controls

sunscreens

melanoma 0-62b

only women aged

et al.32

(0-49-0-83)

25-59 at

(1995)

Superficial

diagnosis. CI

spreading melanoma

estimated. RR for

(SSM) 0-43 (CI not

SSM adjusted for

available)

host factors and

sun exposure

Denmark

Population cases

474 cases

Always used

1-1b (0-8-1-5)

Osterlind

1982-85

and controls

926 controls

sunscreens

et al. (1997)33

Australia

Population cases

50 cases

Always used

2-2 (0-4-12) on

Whiteman

1987-94

Controls from same

156 controls

sunscreens

holidays

et al. (1997)34

Table 23.1 (Continued)

Population

Type of cases/

No. cases/

Exposure

RRa (95% CI)

Comments

Reference

place/date

controls

controls

school

All children < 15

0-7 (0-1-6-0) at school

Sweden 1988-90

Population cases

400 cases

Almost always

Trunk 1-4 (0-6-3-2)

No information on

Westerdahl

and controls

640 controls

used sunscreens

Other sites 2-0 (1-1-3-7)

duration of use

et al. (1995)35

Spain 1989-93

Hospital cases

105 cases

Always used

0-2 (0-04-0-79)

Rodenas

Hospital visitors

138 controls

sunscreens

et al. (1996)36

Spain 1990-94

Hospital cases and

116 cases

Used sunscreen

0-48 (0-34-0-71)

Inadequate

Espinoza-

controls

235 controls

description of measurement of sunscreen use

Arranz et al. (1991)37

Europe 1991-92

Hospital cases

418 controls

Ever use psora-

2-3 (1-3-4-0)

Highest risk for

Autier et al.

Neighbourhood

438 controls

len sunscreens

sun-sensitive

(1995,

controls

Ever use sunscreen

1-5 (1-1-2-1) M 1-8 (1-1-2-7) F 1-3 (0-87-2-0)

subjects using sunscreens to tan: RR, 3-7 (1-0-7-6)

1997b)38

Austria 1993-94

Hospital cases and

193 cases

Often used

3-5 (1-8-6-6)

Wolf et al

controls

319 controls

sunscreen

(1998)39

Sweden 1995-97

Population cases

571 cases

Always used

1-8 (1-1-2-9)

Westerdahl

and controls

913 controls

sunscreen Used sunscreens to spend more time sunbathing

8-7 (1-0-76)

et al. (2000)40

a Relative risk estimates adjusted for phenotype and sun-related factors where possible b Crude relative risk ratio only available melanoma on Intermittently exposed sites (trunk and lower limbs) and controls provided information about the use of sunscreens on these sites during outdoor activity. Risk for those reporting sunscreen "almost always used" was very similar to that of those using sunscreen "sometimes". Those using sunscreen only in first few hours had increased risk after adjustment for hair, eye and skin colouring and propensity to burn.

Holman et al, (1986)31 found that those who had used sunscreens for less than 10 years did not have a reduced risk for cutaneous melanoma: risk was not reduced for those who had used sunscreens for 10-15 years. Frequency of use did not appear to be related to risk. This study did find a positive relationship between the use of sunscreen and the risk for cutaneous melanoma but in the absence of control for pigmentary traits and sun sensitivity. Sunscreens were not available in Australia when the subjects in this study were younger and therefore they were unable to use them at a time when they may have given protection.

Holly et al. (1995)32 found that women who reported "almost always" using sunscreens had a lower risk for cutaneous melanoma than those who reported that they "never" used sunscreens. After controlling for superficial spread of melanoma, sun sensitivity and sunburn history before the age of 12 years the risk for women "almost always" using was lower than for those "never" using. The authors concluded that sunscreen use was strongly protective against melanoma. This study showed that the highest level of risk was for women with the least exposure after controlling for sun sensitivity.

Osterlind et al. (1988)33 found that compared to those who "never" used sunscreens, a small nonsignificant increase in risk was seen for those who had used them for less than 10 years, or for those using for more than 10 years. Frequency of use was not associated with the risk of melanoma among those "always using" against those who "hardly ever used" or "never used". Effective sunscreens were not available to the study group in their youth.

Whiteman et al. (1997)34 found, after controlling for tanning ability, freckling and number of naevi, those who had "always" used sunscreens while on holiday had a non-significant elevated risk for cutaneous melanoma compared to those not using sunscreens. The use of sunscreens at school was associated with a non-significant reduced risk. The RRs have very wide confidence intervals in this study (only 11 "always" used on holiday and only two reported sunscreen use at school).

Westerdahl et al. (1995)35 found, after controlling for history of sunburn; history of sunbathing; number of raised naevi; freckling and hair colour, those "almost always" using sunscreen had similar risk estimates to those "never" using in both men and women. Risk for use before age 15, at age 15-19 and at age 19 years reported elevated odds ratios at each stage similar to those of people "always using" sunscreens. Risk for melanomas of the trunk were similar to that found for melanomas of the extremities, and head and neck, after adjustment for sunburns, frequent sunbathing, freckling and naevi.

Rodenas et al. (1996)36 reported that the use of sunscreen appeared to protect against melanoma and that risk was strongly associated to the sensitivity of the skin to the sun (relative risk of 2-0) for those who always burned. This study failed to give a description of how sunscreen use was measured. Espinoza-Arranz et al. (1999) found similar results.37

Autier et al. (1995 and 1997)38 found that those who had "never" used psoralen-containing sunscreens had an increased risk for cutaneous melanoma after controlling for age, sex, hair colouring, and number of weeks spent in sunny climes each year. An elevated risk was found particularly among those who reported no history of sunburn. Use of psoralen-containing sunscreens, however, was not common. Those "ever" using these sunscreens (psoralen) also had increased risk after adjustment for some factors compared to those "never" using. Increased risk was reported for those using sunscreens and those having light or dark hair. Sensitive and sun-insensitive participants showed an increased risk with the use of sunscreens. The authors concluded that use of sunscreen tended to be associated with higher risk for cutaneous melanoma among sunbathers. Highest risk was for those using sunscreen and who had no history of sunburn after age 14 years. The use of clothing, rather than sunscreen, appeared protective. It was the use of sunscreen, particularly in UVA as well as UVB light, that was found to associated with increased risk.

Wolf et al. (1998)39 reported "often used" sunscreen had a significant higher risk for melanoma compared to "never used" (study controlled for skin colouring, sunbathing and history of sunburn). The authors concluded that use of sunscreen did not prevent melanoma.

Westerdahl et al. (2000)40 reported a significantly increased risk for melanoma for regular use (always used) of sunscreen after adjustment for hair colour, history of sunburns, frequency and duration of sunbathing. Risk was significantly increased among those using sunscreens with an SPF less than 10 compared with those who did not use sunscreens and for those with no history of sunburn when they used sunscreens. The risk was even higher for those using sunscreen to increase sunbathing time (deliberate exposure). In an analysis of subsites, risk was significantly increased only for melanoma of the trunk.

The following studies could be assessed as supporting a positive association between sunscreen use and risk of cutaneous melanoma but this tentative conclusion should be viewed cautiously.26-29,38-40 Confounding factors such as: sunscreen use, sun exposure, sun sensitivity, a history of sun-related neoplasia and sun-protective behaviour such as the use of protective clothing, staying indoors or seeking shade were problematic in these studies. There was idiosyncratic reporting of these confounding factors casting doubt on the significance of the results.

Three studies30,31,33 reported no increased risk for use of sunscreen and cutaneous melanoma with non-significant increase being reported in one study.34 Three studies reported sunscreen as protective against cutaneous melanoma.34,36

Studies that have assessed naevus count as an indicator of melanoma risk

One study using naevi count as an intermediate endpoint showed that the median number of new naevi in Caucasian children was reduced in the sunscreen users. Sunscreen was more effective in preventing naevi in children who freckled than in those who did not.41 Difference in exposure time was not a significant variable. One cohort study42 showed increasing naevi development with sunscreen use. Further analysis showed that this was because children who used sunscreen had longer cumulative exposure time but no data were available to support this conclusion. The cross-sectional study43 reported that the use of summer sunscreen reduced the number of sunburns but was not associated with annual sun exposure or with naevi number or density. This study was criticised for not reporting all data.

Studies using naevus count as an outcome do not provide any conclusive evidence about the relationship between the use of sunscreen and reduced naevi and thus reduced risk for cutaneous melanoma. In all studies the confounding variables and lack of reported data were problematic. A consistent finding of all these studies was the link between cumulative exposure and risk.

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