Transdifferentiation Of Chronic Lymphocytic Lymphoma To Langerhans Cell Sarcoma

DP19 Transdifferentiation of chronic lymphocytic lymphoma to Langerhans cell sarcoma J. Guckian, B. Mathew and S. Clark Leeds Teaching Hospitals Trust, Leeds, UK We detail the case of an 80-year-old man who presented with an unusual right axillary lesion. The patient had a background of chronic lymphocytic lymphoma (CLL); he has been monitored since 2013, but the CLL has been progressive since 2019. He had recently commenced acalabrutinib. This was an atypical appearing, erythematous, smooth, minimally eroded nodule that was 20–25 mm in diameter. The lesion had been rapidly growing for 2 weeks and excision was carried out to rule out a poorly differentiated tumour, with histology reviewed by two different dermatopathology teams. Sections showed a polypoid lesion with focal ulceration. The lesion was composed of sheets of large histiocyte-like cells with illdefined cell membranes. Small areas of tumour necrosis and frequent mitotic figures were seen, including some abnormal forms. On immunohistochemistry the large histiocyte-like cells stained with CD1a, S100, CD4, CD5 and CD56, with patchy staining with CD163. There was no staining for desmin, hCaldesmon, CD10, CD45, smooth muscle actin, MelanA, AE1/ AE3 and MNF116. The staining pattern was of an aberrant Langerhans cell phenotype. There was no staining of the cells to BRAF V00e antibody. The impression was that these findings represented transformation of CLL to Langerhans cell sarcoma in skin. This process of transformation, described as ‘transdifferentiation’, has been noted to be extremely rare in CLL. The mechanisms underpinning this phenomenon are currently unknown, although prior evidence suggests a clonal relationship between CLL and histiocytic/dendritic cell tumours. Previous case reports have highlighted BRAF V00e positivity in such instances, a finding that was negative in this presentation (Cai D, Chen W, Jaffe R et al. Langerhans cell sarcoma arising from chronic lymphocytic lymphoma/small lymphocytic leukemia: lineage analysis and BRAF V600E mutation study. N Am J Med Sci 2013; 5: 386–91). This patient has subsequently been rediscussed with haematology in order to decide appropriate radiotherapy, ahead of likely wide local excision. DP20 Reticular erythematous mucinosis: a rare case of primary dermal mucinosis T. Nasreen, H. Sazali and C. Feighery Our Lady of Lourdes Hospital, Drogheda, Ireland Reticular erythematous mucinosis (REM) is a rare, idiopathic disorder of primary dermal mucin accumulation, characterized by maculopapular reticular erythema or plaques commonly on midline, upper back and chest (Cinotti E, Merlo V, Kempf W et al. Mucinosis: histopathological and immunohistochemical features of 25 patients compared with 25 cases of lupus erythematosus tumidus. J Eur Acad Dermatol Venereol 2015; 29: 689– 97). Histology demonstrates superficial and deep perivascular and periadnexal lymphocytic infiltration with abundant mucin. Other conditions bearing resemblance to REM include lupus erythematosus tumidus (LET), dermatomyositis and scleroderma. Early and correct diagnosis is important to exclude the abovementioned diseases as REM is more benign and has fewer systemic consequences. Common features shared by REM and LET are erythematous plaque-like clinical aspect of lesions. However, photosensitivity – rare in REM – is almost always present in LET. Histologically, REM tends to show more scattered superficial lymphocytes with abundant superficial and deep mucin, less frequent immunoglobulin and reduced complement depositions along the dermoepidermal junction than LET. This suggests the distinction of the two diseases and different pathogenetic mechanisms. We report the case of 26-year-old woman whose REM was found to be correlated with smoking, sun exposure and a hot environment. She had an ongoing pruritic rash on her chest and back for 3 years, with intermittent breast tenderness causing her difficulty in wearing a bra. Her family history was not contributory. Examination demonstrated symmetrical reticular macular erythema on her central back and chest, with some discrete erythematous papules on the medial aspect of the breasts. She remained nonrespondent to topical miconazole, hydrocortisone, fusidic acid and betamethasone valerate. Investigations, including full blood count, serum biochemistry, antinuclear antibody, extranuclear antibodies, and C3 and C4 levels, were normal. Patch test was positive for nickel and fragrance mix. Initial differentials were allergic dermatitis/tumid lupus/REM/ scleroderma. Punch biopsy revealed normal epidermis with superficial and deep perivascular and perifollicular lymphocytic inflammatory infiltrate, with a copious amount of mucin between collagen fibres of the dermis. Mucin stain was positive. A clinicopathological diagnosis of REM was made. Allergic dermatitis was a red herring. She was started on hydroxychloroquine and showed remarkable improvement over a few weeks. This case expands our current knowledge of the clinical presentation of this rare midline dermal disorder of mucinosis, which is often recalcitrant to multiple treatment modalities. Antimalarial treatment is considered the most effective approach. To our knowledge, only a few cases exist on its use in REM.