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Keratoacanthoma is a common cutaneous tumor, of which the benign or malignant potential remains controversial. Keratoacanthoma is often considered as a benign skin tumor, because metastases rarely occur. However, metastases of a keratoacanthoma are reported in literature. Furthermore, development of squamous cell carcinoma in keratoacanthoma is also reported. Besides this, it can histopathologically be difficult or even impossible to distinguish between a well differentiated squamous cell carcinoma and keratoacanthoma. These factors lead to complex therapeutical decisions, that can have large implications for the patient. In this report we present a case of an incompletely excised moderately differentiated squamous cell carcinoma of the left cheek (infraorbital), which was initially diagnosed as keratoacanthoma at the referring hospital. The patient was referred to our multidisciplinary head and neck team. It was decided to perform a re-resection, using a so-called ‘Slow Mohs’-procedure. This re-resection appeared to be incomplete and showed extensive perineural growth. This perineural growth extended along the infraorbital/maxillary nerve via the foramen rotundum, into the sinus cavernosus. This made radical surgical resection impossible. It was decided to treat the patient with adjuvant radiotherapy. This case emphasizes not only the controversy surrounding the benign or malignant nature of a keratoacanthoma and the implications for the patient, but also the importance of an adequate multidisciplinary approach in such complex cases.

A 72 year old man, with Waldenstrom macroglobulinemia, presented with pruritic skin lesions on the trunk (erythematosquamous plaques) and the lower legs (purple nodules). Waldenstrom macroglobulinemia can present not only with cutaneous manifestations of the known lymphoma, but can also present with other cutaneous manifestations. These cutaneous manifestations occur in about 5% of the patients, and these skin changes may arise at the same time as the systemic lymphoma, but can also precede or develop much later. There is usually no clear relationship with possible progression of the systemic lymphoma. The cutaneous manifestations can be divided into I. specific and II. non-specific cutaneous manifestations. The specific ones are rare, and consist of the lymphoplasmocytic B-cell infiltrate. The non-specific cutaneous manifestations are versatile and more common; the most common is the hyperviscosity syndroom because of increased IgM levels in the blood (presenting with,amongst others, swelling of the feet, bleeding of the gums and petechiae of the hands and feet). Other non-specific cutaneous manifestations are cryoglobulinemia associated (including cold urticaria, Raynauds phenomenon and acral cyanosis), caused bij deposition of immunoglobulin, or with unknown etiology such as amyloid depositions, paraneoplastic pemphigus or the Schnitzler syndrome. In this patient, the two clinical presentations showed an histologically similar picture of a dermal lymphoplasmacytic B-cell infiltrate with IgM expression, confirming the diagnosis of a specific cutaneous manifestation of his systemic Waldenstrom macroglobulinemia. Short term treatment with total skin irradiation was unfortunately not effective. He was eventually treated with topical clobetasol ointment with a reasonable response.

Neuroendocrine carcinoma of the skin is generally considered as Merkel cell carcinoma (MCC). Here we present two cases of cutaneous neuroendocrine carcinomas of which one presents clinically and histopathologically as a typical MCC and the other does not. Based on our findings we hypothesize that cutaneous neuroendocrine carcinomas can be divided in two main groups, i.e. the classic MCC CK20 + and a more low-grade neuroendocrine carcinoma CK20-/CK7+.

A 9-year-old girl visited the department of Dermatology with an asymptomatic hypopigmented skin eruption on her upper legs, groins and trunk since 7 years. Histopathological analysis established the diagnosis of hypopigmented mycosis fungoides, a rare subtype of cutaneous T-cell lymphoma which is most commonly seen at younger age. The lesions are successfully treated with clobetasol 0.05% ointment 4 days a week.