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

Abstract

Objectives/HypothesisTo investigate the relationship between handedness and the incidence of squamous cell carcinoma in the external auditory canal (EACSCC).Materials and MethodsSixty‐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.ResultsFifty‐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.ConclusionMechanical 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 EvidenceN/A.

Genetic landscape of external auditory canal squamous cell carcinoma

“…These data all suggest that the mutational patterns of EACSCC mostly resemble those of SCC from other primary sites. Unlike lung SCC or HNSCC, tobacco and alcohol use are unlikely to be major carcinogens of EACSCC; previous clinical studies have reported that chronic inflammation in the external auditory canal induced by habitual ear picking and other mechanical stimuli may cause EACSCC, 37,38 but the exact etiology has remained controversial. In this regard, the mutational pattern of EACSCC in which APOBEC signatures are dominant suggests its link to the mutagenic process associated with chronic tissue damage, as a previous genetic study of aggressive cutaneous SCC demonstrated that chronic inflammation‐induced APOBEC mutagenesis drives carcinogenesis 39 …”

Analysis of the epidermal growth factor receptor/phosphoinositide‐dependent protein kinase‐1 axis in tumor of the external auditory canal in response to epidermal growth factor stimulation

“…Activated EGFR is involved in the pathogenesis and progression of EACSCC the same as HNSCC, 10 but the pathogenesis of EACSCC is not fully understood. EACSCC is often accompanied by a marked inflammatory response and is suggested to be correlated with mechanical stimulations to the EAC 36 . In carcinoma tissues, the close correlation between chronic inflammation and a high risk of carcinogenesis has now been widely confirmed 37 .…”

A retrospective analysis of radiotherapy in the treatment of external auditory canal carcinoma

“…In patients with advanced stages of EACC, facial paralysis is also present and is associated with poor survival. Chronic stimulation, such as habitual ear picking, has also been recognized as an important factor in the carcinogenesis of EACC (3).…”