Two subtypes of estrogen receptors (ERs) have been identified in mammals: ERα and ERβ. Because effective antibodies against ERα proteins are available, expression and localization profiles of ERα proteins have been fully determined. By contrast, the paucity of well-validated antibodies against ERβ proteins has caused confusion regarding their expression and localization profiles, which has severely hindered the progress of ERβ research. Notably, the recent discovery of a monoclonal antibody (PPZ0506) specific for human ERβ proteins and its cross-reactivity to rat and mouse ERβ proteins has stimulated development of ERβ detection systems and the use of these systems to analyze the true localization profiles of ERβ proteins. In our previous studies, we reported the development and optimization of immunohistochemical staining methods for rat and mouse ERβ proteins with PPZ0506. Our immunohistochemical results revealed that rat and mouse ERβ proteins are expressed only in more localized tissues and cells than previously assumed, and further indicated that considerable species differences exist in ERβ expression among humans, rats, and mice. In the present review, we discuss various problems in previous ERβ research, new findings obtained using the PPZ0506 antibody, and prospects for future ERβ research.

We report a case of a cutaneous fistula in a child's toe, along with a review of the literature. The patient was a 5-year-old boy whose mother noticed a depressed region at the base of the right first toe when he was 2 years old. The depression persisted with time, so he was referred to our department. During the initial visit, a cutaneous fistula with a diameter of 1 mm and a depth of 2 mm was observed at the base of the toe. Surgical excision was performed, and histopathological findings demonstratd that the fistula wall consisted of multilayered squamous epithelium with a prominent stratum corneum. Postoperative follow-up showed no recurrence. Cutaneous fistulas can be categorized as congenital or acquired. Congenital ear fistulas are caused by a failure of fusion of the auricular tubercle or remnants of the first branchial cleft during the development of the ear. No congenital cutaneous fistulas have been identified arising solely in the limbs. With regard to acquired fistulas, pilonidal sinus has been reported, as have underlying infections and foreign bodies, but none of these were present in our patient. Pilonidal sinuses can form fistulas, cysts, or granulomas containing hair; they occur predominantly in the sacral region, but rarely in the interdigital area. Eight cases have been reported between the fingers, and three between the toes since 2000, mostly in patients working in hair-related occupations, such as barbers, hairdressers, dog trimmers, and sheep shearers. Hair and wool have been identified within the fistulas in the lesions of those working in these occupations. With interdigital sinuses, it is believed that hair clippings penetrate the skin, causing foreign body reactions that result in fistulas which then spread as the hair repeatedly penetrates the fistulas via abrasions of the surrounding skin. In our patient, neither the affected child nor his family had a history of hair exposure or pet ownership. However, considering the lack of previous reports of congenital cutaneous fistulas of the toes and the unlikelihood of a cutaneous fistula developing naturally in such an anatomical site, we thought the probability of an acquired interdigital pilonidal sinus was high. Cutaneous fistulas occurring in the toes are rarely reported in the literature, and reports of more cases will be necessary to elucidate the pathogenesis of this disease.