Summary Advanced basal cell carcinomas (BCCs) frequently acquire resistance to Smoothened (SMO) inhibitors through unknown mechanisms. Here, we identify SMO mutations in 50% (22/44) of resistant BCCs and show that these mutations maintain Hedgehog signaling in the presence of SMO inhibitors. Alterations include four ligand binding pocket mutations defining sites of inhibitor binding and four variants confering constitutive activity and inhibitor resistance, illuminating pivotal residues that ensure receptor autoinhibition. In the presence of a SMO inhibitor, tumor cells containing either class of SMO mutants effectively outcompete cells containing the wild type SMO. Finally, we show that both classes of SMO variants respond to aPKC-ι/λ or GLI2 inhibitors that operate downstream of SMO, setting the stage for the clinical use of GLI antagonists.

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The authors report six further cases of a cutaneous lymphoid proliferation that share many of the features of a case series previously described as indolent CD8-positive lymphoid proliferation of the ear. Previous reports of this entity have described the slow growth of cutaneous papules and nodules, with a predilection for the ear, associated with specific histopathologic and immunophenotypic features and a benign clinical course. These include the presence of a clear Grenz zone without epidermotropism, and a CD8(+) granzyme B- immunophenotype with a low proliferative index. The current case series presents some atypical clinical features, including site of disease beyond the ear and recurrent disease. Despite this, indolent clinical evolution is apparent. Histopathologically, three of the six cases showed a moderate-high proliferative index, while two cases had very focal epidermotropism and Pautrier collections. A single example had significant granzyme B expression. These previously unreported features add to our understanding of this rare entity, which is not currently recognized in the World Health Organization (WHO)/European Organization for Research and Treatment of Cancer (EORTC) classification.

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