Contribution of stem cells to epidermal and hair follicle tumors in the dog

Background - Although cutaneous stem cells have been implicated in skin tumourigenesis in humans, no studies have been conducted to our knowledge to elucidate the role of stem cells in the development of hair follicle tumours in the dog. Animals and Methods - In the current study, normal skin sections and 44 follicular tumours were retrospectively investigated for the immunohistochemical expression of keratin 15 (K15) and nestin. In addition, 30 squamous cell carcinomas were evaluated for K15 expression. Results - In normal skin, K15 and nestin were expressed in the outer root sheath cells of the isthmic portion of the hair follicle (bulge region) and K15 expression was also scattered in the basal cell layer of the epidermis. Infundibular keratinizing acanthomas, pilomatricomas and squamous cell carcinomas were mostly negative for K15, trichoblastomas were moderately to strongly positive, and trichoepitheliomas had heterogeneous staining. Nestin expression was generally faint in all follicular tumours. Conclusions - Our results show that K15 can be a reliable marker for the study of the role of stem cells in hair follicle tumours of the dog, while nestin was judged a non optimal marker. Furthermore, our study suggests that hair follicle stem cells in the bulge region of hair follicles may play a role in tumourigenesis of canine tumours originating from this portion of the follicle, namely trichoblastomas and trichoepitheliomas. The loss of K15 expression in squamous cell carcinomas compared to normal skin suggests that this event could be critical in the malignant transformation. [...]