SCLC, Paraneoplastic Dermatomyositis, Positive Transcription Intermediary Factor 1-γ, and Point Mutation in the Transcription Intermediary Factor 1-γ Coding Gene: A Case Report.

SCLC is frequently associated with paraneoplastic syndromes, including dermatomyositis. Patients with malignancy-associated dermatomyositis express a specific autoantibody pattern usually positive for anti-transcription intermediary factor 1-γ (TIF1-γ), suggesting anti-TIF1-γ plays a role in development of malignancy-associated dermatomyositis. We present a case of a patient with SCLC, paraneoplastic dermatomyositis, positive anti-TIF1-γ, and a point mutation in TIF1-γ coding gene, with prominent clinical response to chemoradiation. We suggest that this point mutation is pathogenic, providing evidence for the development of paraneoplastic dermatomyositis through immune cross-reactivity.