Sun exposure, prevalence and localization of common melanocytic naevi in Swedish children

Background: The rapidly rising incidence rates of cutaneous malignant melanoma call for more effective prevention strategies. Melanoma susceptibility is associated with having many common melanocytic naevi. Having fair skin, blonde/ash-blonde hair and grey/blue/green eye colour are also joint risk factors for melanoma and naevi. Naevi appear in early childhood and are inducible by sun exposure. As latency between sun exposure and subsequent melanoma development may stretch for decades, naevi prevalence in children has been suggested as a suitable surrogate marker to monitor population trends in sun exposure.

Aims: The aims of this thesis were to analyse the effects of sun exposure and sun protection on naevi prevalence in Swedish children. Further, to review changes in body-site distributions of naevi in response to different patterns of sun exposure and to compare childhood naevi distributions with melanoma localization in adults at different latitudes of residing. The aim was also to validate the feasibility of mobile teledermatology for the remote assessment of naevi prevalence compared with standard manual counting of naevi.

Methods: Naevi prevalence and body-site localizations were investigated in two consecutive population-based cross-sectional studies conducted among 7-year-old children in southern Sweden in years 2002 and 2007. Survey data regarding children’s sun exposures were provided by parental questionnaires. For comparison between childhood naevi and melanoma distributions in northern and southern Sweden, the Swedish Cancer Registry was utilized. Mobile teledermatology was performed with an iPhone 4S camera of naevi on the back of 97 children aged 7-16 years and naevi were counted by standard manual procedure. Inter-method reliability (i.e. mobile teledermatology versus manual counting) and inter-rater reliability (between two independent dermatologists) were calculated with weighted kappa statistic.

Results: Significant improvements in parental sun protective measures for their children were reported in 2007 when compared with 2002. Correspondingly, the total mean number of naevi per child had become significantly lower in 2007. Analysing the body-site specific naevi densities demonstrated that these had become significantly lower solely on intermittently sun exposed body sites, such as the trunk and limbs. The reduction of naevi was largest among boys. Comparisons between melanoma and childhood naevi distributions in northern and southern Sweden demonstrated an almost two-fold higher incidence of melanoma and likewise a higher density of childhood naevi in southern Sweden. Gender profiles and body-site distributions of childhood naevi matched significantly with melanomas in young and middle-aged adults. In southern Sweden slightly more naevi and melanomas were located on the trunk; a body site associated with intermittent sun exposure. Validation of mobile teledermatology imaging for the remote counting of naevi proved substantial for both dermatologists counting naevi from digital images compared with the manual assessment.

Conclusions: In summary, the results of this thesis supported and extended the scientific basis for which naevi in children can be used as objective biomarkers of sun exposure. It also supported childhood naevi to be largely consistent with overall and subsite distributions of melanoma in relation to gender and latitude of residing. Mobile teledermatology proved valid for estimating naevi prevalence on the back and could provide a feasible methodology following trends in sun exposure in children. In a future perspective, assessment of childhood naevi may be implemented in population-based surveillance programs validating the effectiveness of public health campaigns aiming to reduce incidence of melanoma in Sweden.

List of scientific papers

I. M. A. Karlsson, C.F. Wahlgren, K. Wiklund, Y. Rodvall. Sun tanning habits and prevalence of common melanocytic naevi among 7-year-old children in Sweden: changes over a 5-year period. Br J Dermatol. 2011 Apr (164(4);830-7.
https://doi.org/10.1111/j.1365-2133.2011.10214.x

II. M. A. Karlsson, B. Lindelöf, C.F. Wahlgren, K. Wiklund, Y. Rodvall. Mobile teledermatology is a valid method to estimate prevalence of melanocytic naevi in children. Acta Derm Venereol. 2014. Aug 20.
https://doi.org/10.2340/00015555-1950

III. M. A. Karlsson, Y. Rodvall, C.F. Wahlgren, B. Lindelöf, K. Wiklund. Changes in the body-site distribution of common melanocytic naevi among 7-year-old Swedish children between year 2002 and 2007. [Submitted]

IV. M. A. Karlsson, Y. Rodvall, C.F. Wahlgren, K. Wiklund, B. Lindelöf. The anatomic distribution of cutaneous melanoma in adults and melanocytic naevi in children: a population-based study in northern and southern Sweden. [Submitted]