Cutaneous Human Papillomaviruses and Squamous Cell Carcinoma of the Skin: Nested Case–Control Study Free

Immunosuppression greatly raises the risk for nonmelanoma skin cancer (NMSC). Activation of oncogenic skin viruses has been proposed as a possible explanation. Cutaneous papillomaviruses infect healthy skin and are found in skin lesions such as actinic keratosis (AK) and squamous cell carcinoma (SCC) of the skin (1). Prospective human papillomavirus (HPV) seroepidemiology has been instrumental in providing prospective evidence supporting the causal association between HPV and cervical, anogenital, and oropharyngeal cancers (2).

Previously, we reported weak associations between HPV types 3, 15, 38, and 76 and future risk of SCC (3). The previous study was carried out using an HPV serologic method (GST-L1 fusion proteins) that has only weak association with HPV infection (4). Using a conformational HPV antigen (pseudovirions), HPV serology shows a better correlation to HPV infection (4). To use the improved HPV serology for a large prospective study is, therefore, likely to be more informative regarding any possible role of HPV in skin cancer.

The cohorts and the study design are previously described (3). One matched control was selected for each case. We could include 633 SCC cases with 3,115 samples and 1,990 BCC cases with 6,145 samples and the same numbers of controls. In the serial-samples analysis, there were 531 BCC and 256 SCC cases (and the same numbers of controls) that had at least 2 prediagnostic samples.

Serology was performed as described previously (5). Pseudovirions of HPV 3, 5, 6, 11, 15, 16, 18, 31, 32, 33, 38, 45, 52, 58, 68, 76 and Human polyomaviruses Merkel Cell polyomavirus (MCPyV) and JC polyomaviruses (JCPyV) were included (4). Cut-off values to define seropositivity were calculated independently for each HPV type by analyzing the mean fluorescence intensity unit (MFI) values obtained from 141 children's sera (average 4 year old). The cut-off algorithm recommended by the global HPV LabNet (mean MFI value of a negative control serum panel plus 3 SDs; ref. 6) was used, except that the cutoff value had to be at least 250 MFI.

Relative risks were estimated as odds ratios and 95% confidence intervals (CI) by means of conditional logistic regression with SAS 9.4 software (SAS Institute, Inc). If the asymptotic model did not converge, median unbiased estimates of ORs were estimated by exact conditional logistic regression. Heterogeneity in the OR estimates was assessed with a likelihood ratio test.

Seropositivity at baseline showed no association to future risk for SCC for any of the tested viruses and only weak association to BCC for HPV-5 (OR, 1.1; 95% CI, 1.0–1.3), HPV-15 (OR, 1.2; 95% CI, 1.0–1.4), HPV-38 (OR, 1.1; 95% CI, 1.0–1.3), and MCPyV (OR, 1.1; 95% CI, 1.0–1.3; Table 1). All beta-2 HPV types together had a weak association with future BCC (OR, 1.2; 95% CI, 1.1–1.4; Table 1). In analyses restricted to multiple samples, HPV-3 and the alpha-7 HPV group had weak associations with SCC at baseline (OR, 1.8; 95 % CI, 1.0–3.1 and OR, 2.2; 95 % CI, 1.0–4.9, respectively; Table 2). HPV-5 associated with SCC, if seropositivity was acquired during follow-up (OR, 3.2; 95% CI, 1.3–7.6; Table 2). Persistent HPV-6 seropositivity was weakly associated with SCC (OR, 2.2; 95% CI, 1.0–4.8; Table 2) and persistent seropositivity to HPV-15 and the HPV beta-2 group was weakly associated with BCC risk [(OR, 1.4; 95% CI, 1.0–1.9) and (OR, 1.4; 95% CI, 1.1–2.0), respectively; Table 3].

We report a large, prospective HPV serologic study with improved methodology to assess possible associations between HPV infections and future NMSC, as has been reported previously (3). In the current study, we found exactly the same result for HPV-15 and the HPV beta-2 group as in the previous study regarding association with BCC development if seropositive at baseline and for HPV-15 if persistently seropositive. The previously reported associations between HPV-3, 38, 76 or the beta-2 group and SCC (3) were not found in the current study.

All statistically significant associations were very weak and, considering the large number of viruses analyzed, might thus be attributable to chance. The strongest association was seen for acquired HPV-5 seropositivity and future SCC risk. In 2012, IARC classified HPV-5 as having "limited evidence” for carcinogenicity, mostly based on data from the epidermodysplasia verruciformis disease (7). We found that HPV-5 may be involved in skin SCC, also in the general population.

A majority of studied HPV types were genital/mucosal and were included as negative controls. Persistent seropositivity for HPV-6 was weakly associated with future SCC, most likely attributed to chance. As we only studied four different HPV types in the beta group, we cannot conclude that all cutaneous HPV are harmless. For example, a recently discovered HPV type (HPV-197) has been reported in a rather large proportion of SCC (8). Continued analysis of possible association between cutaneous HPV and skin cancer, using extended panels with additional pseudovirions from new HPV types may be warranted.

No potential conflicts of interest were disclosed.

Conception and design: K. Andersson, J. Dillner

Development of methodology: H. Faust, J. Dillner

Acquisition of data (provided animals, acquired and managed patients, provided facilities, etc.): H. Faust, K. Andersson, R.E. Gislefoss

Analysis and interpretation of data (e.g., statistical analysis, biostatistics, computational analysis): H. Faust, K. Andersson, T. Luostarinen

Writing, review, and/or revision of the manuscript: H. Faust, K. Andersson, T. Luostarinen, R.E. Gislefoss, J. Dillner

Administrative, technical, or material support (i.e., reporting or organizing data, constructing databases): T. Luostarinen

Study supervision: J. Dillner

The authors acknowledge financial support from the Swedish Cancer Society. The authors thank Christina Cavala for excellent technical assistance.

J. Dillner has received financial support from the Swedish Cancer Society for this study.

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