Right dominance in the incidence of external auditory canal squamous cell carcinoma in the Japanese population: Does handedness affect carcinogenesis?

OBJECTIVES/HYPOTHESIS: To investigate the relationship between handedness and the incidence of squamous cell carcinoma in the external auditory canal (EACSCC). MATERIALS AND METHODS: Sixty-eight cases of EACSCC were enrolled in this study, and their affected side was checked. Handedness and ear-picking habits were also investigated in 34 EACSCC cases. Handedness was judged based on self-categorization, and the relationship between handedness and the affected side was investigated. RESULTS: Fifty-two cases occurred on the right side, and 16 cases occurred on the left side of patients with EACSCC. The incidence of laterality in EACSCC showed a statistically significant right dominance. Concerning handedness, 29 cases were right-handed, 4 cases were left-handed, and 1 case was ambidextrous. Twenty-seven out of the 29 right-handed cases and 1 ambidextrous case suffered from carcinoma on the right side, whereas 3 left-handed cases suffered from carcinoma on the left side. That is, most of the cases suffered from EACSCC on the same side as their handedness, and this tendency showed a statistically significant difference. Most of the patients with EACSCC experienced itching and habitual ear-picking in the affected side. CONCLUSION: Mechanical stimulations to the EAC, such as ear picking, may plausibly cause EACSCC. In Japan, ear picking, also called "mimikaki," is a popular habit and an established unique culture. Because ear picking requires delicate handling and manipulation, this tends to occur on the same side as the handedness in the Japanese population. This is the first report about the relationship between handedness and carcinogenesis. LEVEL OF EVIDENCE: N/A.