P023 Metastatic basal cell carcinoma with bone marrow involvement: a rare case report

Abstract Basal cell carcinoma (BCC) is the most common human cancer, with an estimated annual incidence of over 15 000 cases in Ireland and over 160 000 cases in the UK. Distant metastasis remains exceedingly rare, with approximately 350 reported cases worldwide. Histological confirmation of metastatic BCC is often challenging due to inconsistencies in documentation and analysis of primary and metastatic lesions. Since 2012, inhibitors of the hedgehog signalling pathway, such as vismodegib, have emerged as effective treatment options for locally advanced and metastatic BCC, showing a 37% objective response rate in the STEVIE trial and 43% in the ERIVANCE trial. Our case is a 75-year-old woman who underwent excision of a mixed nodular and infiltrative BCC from her right cheek in 2022, followed by re-excision due to a positive margin. One year later, she experienced a recurrence requiring wide excision, including zygomatic and masseter muscle removal, and adjuvant radiotherapy. Two months after radiotherapy, she presented with pancytopenia and a leucoerythroblastic blood smear. A bone marrow biopsy revealed extensive infiltration by metastatic carcinoma. Comprehensive investigations, including computed tomography (CT) imaging, positron emission tomography–CT, and endoscopic examinations, failed to identify another primary malignancy. Histopathological comparison confirmed morphological similarity between the metastatic deposits and the previously resected BCC. This case highlights the rare but significant potential for BCC to metastasize, even following adequate local treatment and radiotherapy. The patient’s presentation with pancytopenia underscores the importance of considering metastatic BCC in cases of unexplained haematological abnormalities in patients with a history of aggressive BCC. Systemic therapies such as vismodegib offer a targeted treatment option and represent a significant advancement in managing metastatic BCC.