Disseminated Mycobacterium kansasii infection revealing GATA2 haploinsufficiency after presumed tuberculosis and early lung cancer.

A 46-year-old previously healthy and asymptomatic woman was incidentally found to have right lung opacities after a traffic accident. Histology revealed chronic granulomatous inflammation, leading to an initial diagnosis of tuberculosis with partial response to treatment. A persistent right upper lobe nodule was later confirmed as minimally invasive lung adenocarcinoma. Post-wedge resection, she developed recurrent fever, dyspnea, weight loss, leukopenia, and monocytopenia. Subsequent PET revealed marked mediastinal lymphadenopathy, and mycobacterial cultures of biopsied lymph nodes and bone marrow yielded Mycobacterium kansasii. Further immunologic evaluation identified B-cell and NK-cell deficiency without detectable anti-interferon-gamma autoantibodies. Genetic testing uncovered a novel heterozygous GATA2 mutation, establishing a diagnosis of MonoMAC syndrome. Notably, one asymptomatic sister carried the same pathogenic variant. This case highlights the importance of considering GATA2 haploinsufficiency in adults with atypical mycobacterial infections and cytopenias. Early recognition enables targeted infection surveillance, multi-system assessment, family genetic counseling, and definitive hematopoietic stem cell transplantation planning when indicated.