Background A recent review of the SEER database revealed that melanoma and Merkel cell carcinoma occur more commonly on the left side of the body. Similarly, a trend was reported in which nonmelanoma skin cancers (NMSCs) were found to be distributed more frequently on the left side of the body. Objectives To compare the sidedness of NMSC in a large patient population. There were five primary objectives of the present study: (i) to confirm or refute the left-sided trend of NMSC in the largest patient population studied for asymmetry to date; (ii) to determine whether the left-sided trend existed in Hispanic/Latino individuals; (iii) to examine skin cancer in older individuals across ethnicities; (iv) to compare distribution across anatomical location and ethnicity; and (v) to measure gender differences in the distribution of NMSC. Methods The last 3026 cases referred to the Mohs surgical unit at the University of Miami Miller School of Medicine during 2008-2011 were reviewed. The patient's age, gender, tumour side, tumour type, anatomical location and ethnicity were recorded. Results There were 1505 (50·2%) right-sided tumours and 1495 (49·8%) left-sided tumours (P = 0·52). The Hispanic/Latino group had a nonsignificant right-sided trend with 607 (52·7%) right-sided cases and 545 (47·3%) left-sided cases (P = 0·06). The non-Hispanic/non-Latino group between the ages of 60 and 85 years had 605 (46·9%) right-sided tumours and 686 (53·1%) left-sided tumours (P = 0·024). The Hispanic/Latino group between the ages of 60 and 85 years demonstrated 404 (54·0%) right-sided tumours and 344 (46·0%) left-sided tumours (P = 0·028). One hundred and fifty-four skin cancers were located on the upper extremities of non-Hispanic/non-Latino individuals with 64 (41·6%) being right sided and 90 (58·4%) left sided (P = 0·036). Seventy-eight skin cancers were located on the upper extremities of Hispanic/Latino individuals with 49 (62·8%) being right sided and 29 (37·2%) left sided (P = 0·024). Males had most of the skin cancers at 2125 (70·8%) cases and females had 875 (29·2%) cases (P < 0·001). Conclusions NMSC appears to be more common on the left side of older non-Hispanic/non-Latino individuals, while it is more common on the right side of older Hispanic/Latino individuals. This is likely to be secondary to an environmental factor, such as ultraviolet radiation. NMSC is significantly more common in males relative to females, which may be attributed to differences in gender roles or referral practices.
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