Benign and malignant tumours may arise from eccrine and apocrine sweat glands. Hidradenocarcinoma is a rare malignant eccrine sweat gland tumour representing <0.01% of all skin cancers. There are 6 case reports in the literature of hidradenocarcinoma arising on the vulva, none of which are classified as poroid hidradenocarcinoma. Hidradenocarcinoma is thought to be an aggressive tumour with poor prognosis and high levels of local recurrence and systemic metastases. Conversely, hidradenoma papilliferum is a common benign apocrine sweat gland tumour found on the vulva. The prevalence and significance of atypical changes, however, is unknown. Distinguishing between these tumour types can be difficult. The authors present two cases, a poroid hidradenocarcinoma and an atypical hidradenoma papilliferum with necrosis and increased mitotic activity, to illustrate the diagnostic challenges associated with rare tumours of the vulva in the absence of an established histopathological classification system.

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example of Langerhans cell sarcoma transdifferentiating from a follicular lymphoma and will discuss the limited literature in this rare entity. The role of BRAF V600E mutation in prognosis and treatment will also be discussed. References 1. West DS, Dogan A, Quint PS, et al. Clonally related follicular lymphomas and Langerhans cell neoplasms; expanding the spectrum of transdifferentiation. Am J Surg Pathol 2013; 37: 978-86. 2. Wu Y, Chen WY, Yang TX, et al. Langerhans cell sarcoma arising from antecedent Langerhans cell histiocytosis; a case report. Medicine 2019; 98: e14531. 3. Zeng K, Wang Z, Ohshima K, et al. BRAF V600E mutation correlates with suppressive tumor immune microenvironment and reduced disease-free survival in Langerhans cell histiocytosis. Oncoimmunology 2016; 5: e1185582.