Australasian Journal of Dermatology

(2003)

44

,

34–39

Correspondence: Dr Robert H Rosen, Southern Suburbs Derma-tology, 40 Montgomery St, Kogarah, NSW 2217, Australia. Email:skindoc@bigpond.net.au

Robert H Rosen, FACD. Howard Studniberg, FACD.Dr Rosen has worked as a consultant for 3M Pharmaceuticals.This paper is based on an oral presentation given at the Annual

Scientific Meeting of the Australasian College of Dermatologists inAdelaide in May 2001. It has been awarded the FC Florence–EwanMurray Will grant. This study was also assisted with a grant from 3MPharmaceuticals.

Submitted 20 July 2001; accepted 7 September 2002.

RESEARCH REPORT

Solar keratoses: Analysis in a dermatological practice in Australia

Robert H Rosen and Howard Studniberg

Southern Suburbs Dermatology, Sydney, New South Wales, Australia

INTRODUCTION

The risk factors for solar keratosis (SK), squamous cellcarcinoma (SCC) and basal cell carcinoma (BCC) are almostidentical and the population involved often suffers from allthree cutaneous tumours.

1

It has been estimated that asmany as 10% of SK will progress to SCC

2

and up to 97% ofSCC are associated histologically with a contiguous SK.

3

People with more than 10 SK have a 14% chance ofdeveloping a SCC within 5 years.

4

Their presence alsoidentifies a population at risk of BCC.

2

However over a 12-

month period up to 25% of SK may resolve with regular useof sunscreen.

5

In Australia 45% of the population older than 40 years ofage has been found to have SK,

6

the reported average numberbeing eight.

1

Men have a greater prevalence than women,particularly in the younger decades.

7

Solar keratoses aremost numerous on sun-exposed sites and occur morefrequently on the upper limbs than on the face, ears or neck.

7

It has been pointed out, however, that SCC occur pre-dominantly on the head and neck and not the upper limbs.

8

This discrepancy has not been satisfactorily explained.It is suspected by the authors that patients seen by derma-

tologists have much more extensive sun-damage-relateddisease than is generally represented in population-basedstudies and frequently have coexisting non-melanoma skincancer (NMSC).

1,7

A study was undertaken of 200 consecutive patientspresenting to dermatologists in private practice for examin-ation

and

treatment

of

SK,

in

order

to

define

the

extentof actinic damage currently seen by dermatologists inAustralia.

METHODS

Patients referred to a specialist dermatology practice weregiven thorough skin examinations by one of three derma-tologists. The practice is located in the southern suburbs ofSydney, approximately 15 km from the city centre, but drawspatients from all over New South Wales.

Patients were referred for assessment and treatment ofsolar damage. This included patients known to have SK and/or NMSC, as well as patients who presented for generaldermatological evaluation. The patients were required tohave at least one SK to enter the study.

The site of the SK and the number of SK per region werecollated. The number of SK present were assessed in fiveranges: 0, 1–10, 11–20, 21–30 and >30. The last grouprepresents a ‘field defect’ where extensive actinic damageresults in regions of skin where SK seem to merge togetherand cannot be isolated clearly enough to be counted indi-vidually. Indeed, 30 may be an underestimate in many areaswhere there are ‘field defects’, except for particularly smallareas such as the nose.

The head and neck area was divided up into smallerregions because of their relative importance. The upper limb

SUMMARY

Two hundred consecutive patients with solar keratoses(SK) seen in a private dermatology practice had onaverage 61.9 SK compared with eight reported in thegeneral population. Non-melanoma skin cancer waspresent in 41% of patients and 17% had squamous cellcarcinoma (SCC). The ratio of basal cell carcinoma toSCC in the cohort was 1.7:1. The commonest site of SKwas the upper limbs but the greatest density of lesionswas on the face, particularly the nose. Squamous cellcarcinomas were most commonly found on the upperand lower limbs. Basal cell carcinomas were mostcommon on the head and neck.

Key words: actinic damage, actinic keratosis, basalcell carcinoma, cumulative sun exposure, fielddefect, non-melanoma skin cancer, squamous cellcarcinoma.

Solar keratoses seen by dermatologists 35

was recorded as a single location whereas the lower limbwas divided into two units; thighs and legs.

Patient demographics, such as age, sex and whether a newor an existing patient, were recorded. Patients were dividedinto three age groupings, namely, older than 65 years (theretirement age in Australia) and two younger groups ofworking-age adults of 35–50 and 51–65 years.

Past treatments that the patients had received were alsodocumented to give an overview of current practices. Thetreatment options were cryotherapy, curettage and cautery,topical 5-fluorouracil, chemical peeling and laser resur-facing.

The location and number of concurrent SCC and BCCwere recorded. These NMSC were diagnosed clinically.However, in those cases where the lesions were removedsurgically (most lesions) histological confirmation of thediagnosis was obtained and, in cases where the diagnosiswas in doubt and a biopsy taken, histological diagnosis wasrecorded.

The data were then transferred to a computerized spread-sheet where data analysis was performed. Statistical analysisof the results was conducted by Jones and Just Pty Ltd(Sydney, Australia). Correlation between SK and NMSCcounts was assessed using the Spearman rank correlationbecause of the non-normal distribution of the data.

The average number of SK for each region of skin for thethree age ranges as well as for men and women in the studypopulation were calculated.

As the surface areas of skin on the face and on the limbsdiffer greatly, an accurate comparison of severity of actinicdamage can only be made using numbers of SK per unitarea.

It has been estimated that on average the human skincovers an area of 2.0 m

2

.

9

Approximate dimensions of eachbody area rate the head and neck as 9%, the torso (front andback) as 36%, the genitals as 1%, the arms (together) as 18%and the legs as 36% (together).

10

The head and neck can befurther subdivided into the neck 3%, the scalp 3% and theface 3%.

10

The face can be further subdivided into theforehead as approximately 1%, the area of both cheeks as 1%,the chin and lips as 0.5% and the nose 0.5%. The density ofSK in each region was determined by dividing the averagenumber of SK in each body site by the calculated surfacearea of skin

RESULTS

Patient demographics: Age and sex

There were 115 men (57.5%) and 85 women (42.5%) in the200 patients assessed for SK. The age range was 37–96 years.When the three age groups were compared (35–50, 51–65and older than 65 years) it was found that 65% of patientswith SK were older than 65 years. Although more men wereaffected than women overall (57.5:42.5%), this trend wasreversed in the youngest age group where there were 14women to nine men (56:36%).

New or current patients and past therapy

There were 70 newly referred patients (35%) compared with130 (65%) existing patients. In this study, 187 patients hadpreviously had treatment with liquid nitrogen cryotherapy

Figure 1

Most common site of at least one solar keratose comparedbetween the three age groups. (

�

) 35–50 years old, (

�

) 51–65 yearsold, ( ) more than 65 years old.

Table 1

The average numbers of solar keratoses at each site in total as well as for the three age ranges and for men and women, enablingcomparison between these groupings

Site All sites Scalp, ears Forehead Nose Cheek Lips, chin Neck Upper limbs Torso Lower limbs

†

Age 35–50 years 12.6 8.4 8.4 6.8 6.8 5.5 12.7 10.5 21.9Age 51–65 years 12.2 10.7 6.1 8.7 6.3 5.5 15.0 7.8 21.4Age 65 years plus 13.6 12.8 8.7 11.0 6.2 8.4 16.8 10.2 22.4Women 6.2 9.3 7.9 8.3 6.0 8.6 15.4 5.8 19.3Men 14.3 13.4 8.4 11.2 6.7 7.1 16.3 10.5 23.2Total 61.9 13.2 11.8 8.1 10.0 6.3 7.6 15.9 9.7 22.3

†

Thighs and legs combined to form one site: lower limbs. Calculation of average number of solar keratoses (SK) for a given site and agegroup. The total number of SK for a site was first determined by multiplying the number of people who had SK in a range by the mediannumber for that range (5.5 for range 1–10, 15.5 for range 11–20 etc. and 30 for the ‘field defect’ range) and then adding together the median SKfigures for each range. The total number of SK for that site divided by the total number of patients in each age group gave the average numberof SK for a given age group and site (e.g. 35–50-year-olds with SK on the nose).

36 RH Rosen and H Studniberg

(93.5%), 56 patients had previously had curettage andcautery

(28%),

five

patients

(2.5%)

had

applied

topical5-fluorouracil therapy for SK on the face. Only one patienthad undergone laser resurfacing treatment.

Number of patients with solar keratoses at each site (commonest site of solar keratoses)

The commonest site of SK across all age groups was foundto be the upper limbs (Fig. 1). However, if the subclassifi-cations of the face are merged and the figures for the regionsof forehead, nose, cheek, chin and lip added together andthen compared to the figures for upper and lower limbs, thenthe face is by far the commonest region where peopledevelop at least one SK.

Figure 1 shows that 60% of the patients in the older than65 years age group had SK on the scalp, compared with only30% of those aged 35–50 years. In comparison, the sun-exposed sites of the arms, forehead, nose and cheeks wereaffected in 70–80% of patients.

Areas with largest number of solar keratoses

Analysis of the average number of SK per site is shown inTable 1. The average number of SK over all sites was 61.9 perpatient.

For most sites the patients over 65 had more SK than theyounger patients. However there were no significantdifferences between the three age groups.

The areas of greatest solar damage (as determined by theaverage total number of SK per patient) was the lower limbs(legs and thighs) followed by the upper limbs (Table 1). Onceagain, if total SK in the subdivisions of the face are addedtogether and this figure compared with the combined limbsfigure, the count is greater on the face. As the surface area ofthe skin on the limbs is much greater than that on the face,

density of SK (SK per unit area) is a more appropriate wayof comparing the two regions.

Density of solar keratosis distribution

The

density

of

SK

was

found

by

dividing

the

averagenumber

of

SK

as

in

Table 1

by

the

unit

area

of

eachbody

location.

A

comparison

of

regional

density

of

SKis seen in Figure 2. Although the greatest number of SK arefound on the lower limbs followed by the upper limbs(Table 1), the greatest density of SK is found on the sub-regions of the face.

Comparison of solar keratosis distribution between sexes

The average number of SK in each region for men andwomen is shown in Table 1. On average men had more SKthan women both in total as well as at most sites.

Comparison of numbers of solar keratoses in patients with concurrent squamous cell carcinoma and basal cell carcinoma

Skin cancers were present in 82 (41%) of the study patients.Fifty-two

patients

had

73

BCC.

Men

tended

to

havemultiple

BCC,

with

32

having

51

BCC

(70%

of

thetotal BCC) (range 1–8). Twenty women had 22 BCC (30% oftotal). Thirty-four patients had 43 SCC. There were 11women with 12 SCC (28%) and 23 men with 31 SCC (72%).Only four people had both BCC and SCC. Men had skincancers with more than twice the frequency of women. Theratio of BCC to SCC in all patients (all with coexisting SK)was 1.7:1 (73:43).

The number of SK was not increased in those patients withBCC (Fig. 3). There was a non-statistically significant trendfor an increased number of SK in those with SCC (Fig. 4).Most of the SCC were located on the lower limbs (17) andupper limbs (11), which is consistent with the site of greatest

Figure 2

This figure compares the

density

(average

number

ofsolar keratoses/cm

2

) between sites. It indicates how severely eachregion has been damaged.

Figure 3

Comparison of average number of solar keratoses (SK) in(–

�

–) patients with basal cell carcinoma (BCC) and (–

�

–) those with-out BCC.

Solar keratoses seen by dermatologists 37

average number of SK (22.3 and 15.9, respectively). Basal cellcarcinomas were more commonly found on the head andneck (38) than were SCC (13). Basal cell carcinomas werealso more prevalent on the torso (22) than were SCC (two).Although both SCC and BCC occur in sites of solar damage,there is a very different site distribution of the two tumours(Fig. 5).

DISCUSSION

Health Insurance Commission Medicare statistics show thatin 1997–98 dermatologists claimed approximately 40% of thespecified item number for treatment of more than 10 SK.(Pers. comm., Medicare statistics provided for servicesprovided by each medical group between 1 July 1997 and30 June 1998 to R Rosen, 2001). Although not reflected bythese statistics, it is likely that dermatologists treat even morepatients with SK, as they are more likely to use treatmentsother than liquid nitrogen cryotherapy for patients withfewer than 10 SK than non-dermatologists. The statistics areconsistent with the findings of this study. The averagenumber of SK found on patients presenting to a dermatologypractice (61.9) was considerably higher than the averagenumber found in the general population.

1

As expected from prevalence studies,

7

more men had SKthan women both in total number and at most sites and SKnumbers increase with age.

7,11,12

The exception was the neck,and this may reflect differences in attire and daily activity.While women may have longer hair than men, whichprovides some protection, they usually wear ‘open necked’garments that expose the anterior neck and upper chest tothe sun. Women also tend to wear make-up, which mayinclude UV protection, on their face but not the neck. Men, incontrast, tend to have short hair and to wear collar and tie or‘round collared’ T-shirts, affording some protection to theupper chest.

Most of the patients in this study were in the older, post-retirement age range (65%) drawn from the study range of35–92 years

of age. This may reflect a lag period of20–30 years of chronic solar damage before developmentof SK.

The commonest site of SK was the upper limb. This trendwas equal across all age ranges and is consistent withprevious studies,7,13 but may be misleading, as when sub-regions are incorporated into one location (for exampleadding together the total number of SK for all the sub-divisions of the face) the result is different. Furthermore, thedegree of actinic damage in these sites is not reflected bynumber of SK per region, but rather by density of SK perregion.

Only 32% of the younger patients had SK on the scalpcompared with 60% of the patients older than 65 years. Thiscould be because of greater hair coverage in the youngergroup. The older group of patients might be expected to havemore SK than the younger group because of the trendtowards hair loss in men with increasing age, but in thisstudy the average number of SK on the scalp appears to besimilar in both groups. This may be because of the ears beingincluded with the scalp in the statistical analysis andyounger men might be expected to have SK on the ears. Itmay also be as a result of an aberration in the statisticalanalysis whereby even one SK on the ear is counted as 5.5.In addition, it is also possible that the older patients attendmore regularly to have their SK treated.

The findings of this study highlight that the commonestsites of occurrence of SK do not necessarily reflect the extentof solar damage in these areas. The greatest number of SKwas found on the lower limbs, followed by the upper limbs,which reflects the large skin surface areas of these sites.

The greatest density of SK was found to be on the nose andall subregions of the face had greater density of SK, andtherefore actinic damage, than the scalp, followed by theupper limbs and then the lower limbs. This is a significantfinding, as concentrated damage or a ‘field defect’ is the mostdifficult to treat and is most frequently found on the sub-regions of the face.

The major aetiological factor in the formation of SK andNMSC has been identified as ultraviolet (UV) light exposure

Figure 4 There is generally a greater average number of solarkeratoses in (–�–) patients with squamous cell carcinoma (SCC)compared with (–�–) patients without SCC.

Figure 5 Compares numbers and location of (–�–) basal cellcarcinoma and (–�–) squamous cell carcinoma.

38 RH Rosen and H Studniberg

and the basis of variation between locations is the extent ofUV-induced damage at each site.1,3,6–8,11,14 The finding thatdensity of SK is greatest on the face is therefore consistentwith the past conclusion that, for both sexes, the highest ratesof cumulative sun exposure per unit area were on the face.13

Forty-one per cent of the study population had concurrentNMSC, with 26% having BCC, 17% SCC and 2% having both.The total number of NMSC in our cohort was 116 (73 BCCand 43 SCC) representing 58%, whereas in an unselectedpopulation the incidence of NMSC in Australia was 1% (1000per 100 000 people).15 This result supports the importance ofSK as a risk factor. The second national survey of NMSC inAustralia15 showed a general ratio of BCC : SCC of 3:1,whereas in our cohort of patients the ratio was closer to 3:2.This is a result of the selection bias of the study, as SK areknown to progress to SCC and not BCC and therefore moreSCC are expected.2,3,6,11,14–16

Our study showed that SCC were more commonly foundon the upper limbs and lower limbs, which corresponds tothe site of the greatest number of SK. In contrast, a previousstudy8 showed more SCC on the head and neck. Basal cellcarcinomas were most often located on the torso, forehead,cheeks and nose in our study. A discrepancy in the frequencyof SCC and BCC in the heavily sun-exposed areas of theneck, ears and scalp has been reported.13 In that study theincidence rates of SCC in men, but not in women, on thehead and neck, were much higher than for BCC relative tothe whole body. This variation in location of NMSC despite asimilar aetiology of UV exposure14,17–19 has been attributed todifferences in the nature and pattern of UV exposure.Chronic exposure to a constant degree of sunlight, whichresults in tanning and thickening of the skin, protects thedeeper epidermal layers and results in SK and SCC form-ation in higher layers.20–22 This type of UV exposure is oftenoccupational and so affects the limbs predominantly. Incontrast, short bursts of high-intensity sunlight, which mayoccur recreationally on holidays and weekends, result inBCC on the torso because the natural defence of tanning hasnot had the opportunity to protect the basal cells of the

epidermis from solar radiation.20–22 Facial skin actinicdamage may reflect both patterns of UV exposure.

This study demonstrates that the extent of SK in patientspresenting to dermatologists is far greater than that seen inthe general population. The average number of SK in thedifferent body regions as well as their density in this groupof patients suggest that there is a population of Australianswith severe sun damage at increased risk of NMSC. In thesepatients, SK should not be regarded merely as an individuallesion but as part of a more diffuse disease requiring frequentand expert dermatological evaluation. Detailed current dataon SK are summarized in Table 2. Frequent and expertdermatological evaluation is important in this group ofpatients.

ACKNOWLEDGEMENTS

We wish to acknowledge the assistance of Dr Kate Dunlopwho assisted in the assessment of patients and Mr MladenKovac from 3M who arranged statistical assessment of thedata by Jones and Just Pty Ltd (statistical consultants).

REFERENCES

1. Marks R. Epidemiology of non-melanoma skin cancer and solarkeratosis in Australia: A tale of self-immolation in Elysian fields.Australas. J. Dermatol. 1997; 38 (Suppl. 1): S26–9.

2. Dobson JM, DeSpain J, Hewett JE, Clark DP. Malignant potentialof actinic keratoses and the controversy over treatment: Apatient-oriented perspective. Arch. Dermatol. 1991; 127:1029–31.

3. Hurwitz RM, Monger LE. Solar keratoses: An evolvingsquamous cell carcinoma: Benign or malignant? Dermatol.Surg. 1995; 21: 183–6.

4. Moon TE, Levine N, Cartmel B, Bangert JL, Rodney S, Dong Q,Peng YM, Alberts DS. Effect of retinol to prevent squamous cellskin cancer in moderate-risk subjects. Cancer Epidemiol.Biomarkers Prev. 1997; 6: 949–56.

5. Mark R, Foley P, Goodman G, Hage B, Selwood TS. Spontaneousremission of solar keratosis: The case for conservative manage-ment. Br. J. Dermatol. 1986; 115: 649–55.

Table 2 Summary of current data on solar keratosis.

Generation time ?20–30 yearsSelf resolution 25%5

Progression to SCC ?2,16 10%Prevalence 45% in over 40 years age group,6

Average number per person in general population of patients with SK 6–81

Average number in dermatology patients† 61.9Commonest site (at least one SK)† Upper limbs, foreheadGreatest number of SK† Lower limbs, upper limbsGreatest density of SK† NosePrevalence of NMSC in patients with SK† 41%Prevalence of SCC in patients with SK 17%Ratio of BCC : SCC in general population 3:1Ratio of BCC : SCC in patients with SK† 3:2Commonest treatment† CryotherapyAetiology Chronic solar exposure as opposed to sunburn19–21

†Statistics from this study undertaken in a private dermatological practice. BCC, basal cell carcinoma; NMSC; non-melanoma skin cancer;SCC; squamous cell carcinoma; SK, solar keratoses.

Solar keratoses seen by dermatologists 39

6. Marks R, Jolley D, Lecatsas S, Foley P. The role of childhoodsunlight exposure in the development of solar keratoses andnon-melanoma skin cancer. Med. J. Aust. 1990; 152: 62–6.

7. Frost CA, Green AC. Epidemiology of solar keratoses. Br. J.Dermatol. 1994; 151: 455–64.

8. Salasche SJ. Epidemiology of solar keratoses and squamous cellcarcinoma. J. Am. Acad. Dermatol. 2000; 42 (Suppl.): S4–7.

9. O’Rahilly R. Skin, hair and nails. In: Gardner E, Grey D,O’Rahilly R (eds). Anatomy, 4th edn. Philadelphia: WBSaunders, 1975; 46–61.

10. Huckstep RI. Assessment of burns. In: A Simple Guide toTrauma, 3rd edn. Edinburgh: Churchill Livingstone, 1982;102–8.

11. Holman CD, Armstrong DK, Evans PR, Lumsden GL, DallimoreKJ, Meehan CJ, Beagley J, Gibson IM. Relationship of solarkeratoses and history of skin cancer to objective measures ofactinic skin damage. Br. J. Dermatol. 1984; 110: 129–38.

12. Green A, Beardmore G, Hart V, Leslie D, Marks R, Staines D.Skin cancer in a Queensland population. J. Am. Acad. Dermatol.1988; 19: 129–38.

13. Franceschi S, Levi F, Randimbison L, La Vecchia C. Sitedistribution of different types of skin cancer: New etiologicalclues. Int. J. Cancer 1996; 67: 24–8.

14. Armstrong BK, Kricker A, English DR. Sun exposure and skincancer. Australas. J. Dermatol. 1997; 38 (Suppl. 1): S1–6.

15. Marks R, Staples M, Giles GG. Trends in non melanoma skincancer treated in Australia: The second national survey. Int. J.Cancer 1993; 53: 585–90.

16. Glogau RG. The risk of progression to invasive disease. J. Am.Acad. Dermatol. 2000; 42 (Suppl.): S23–4.

17. Unna PG. Die Histopathologie der Hautkrankheiten. Berlin.Verlag von Ausgust Hirschwald; 1894, 665–747 (In German, noabstract in English).

18. Kricker A, Armstrong BK, English DR. Sun exposure and nonmelanocytic skin cancer. Cancer Causes Control 1994; 5:367–92.

19. Armstrong BK, Kricker A. Epidemiology of sun exposure andskin cancer. Cancer Surv. 1996; 26: 133–53.

20. Kricker A, Armstrong BK, English DR, Heenan PJ. Doesintermittent sun exposure cause basal cell carcinoma? A casecontrol study in Western Australia. Int. J. Cancer 1995; 60:489–94.

21. Rosso S, Zanetti R, Martinez C, Tormo MJ, Schraub S, Sancho-Garnier H et al. The multicentre south European study‘Helios’II: Different sun exposure patterns in the aetiology ofbasal cell carcinoma of the skin. Br. J. Cancer 1996; 73: 1447–54.

22. Strickland Vitas BC, West SK, Rosenthal FS, Emmett EA, TaylorHR. Quantitative carcinogenesis in man: Solar ultraviolet B dosedependence of skin cancer in Maryland watermen. J. NatlCancer Inst. 1989; 81: 1910–13.