MAC Attack: Clinical Correlates of Mycobacterium avium Complex Infection Among Patients With and Without Cancer

In 2007 the American Thoracic Society (ATS) released guidelines on management of Mycobacterium avium complex (MAC), an increasingly common respiratory organism worldwide. Determining when this represents a true respiratory pathogen remains controversial and becomes increasingly challenging in patients with cancer. This study aims to 1) describe the phenotype that exists among cancer patients with MAC colonization and MAC pulmonary infection when compared to non-cancer patients; 2) assess whether cancer, symptoms, and radiographs, were associated with the decision to treat MAC pulmonary infection with antibiotics.

We retrospectively analyzed 550 adult, non-human immunodeficiency virus (HIV) patients, among whom MAC was identified in respiratory cultures or tissue. Radiographs, clinical symptoms and cancer status were studied. Patients were categorized as having MAC pulmonary infection based on 2007 ATS guidelines, and antibiotic treatment was thereafter reviewed. Fisher's exact test and Wilcoxon Rank sum assessed differences.

Median age of the 550 patients was 68 years; most were female (56%) and white (83%). Symptoms and radiographic abnormalities accompanying MAC isolation were common, occurring among 83% and 99.6% respectively of all patients. There were 444 patients with MAC who had current or inactive cancers, most commonly hematologic (30%) and lung (25%) malignancies, while 106 patients never had cancer. Cancer patients were younger (P = 0.028), less often female (P < 0.001), and had less-frequent pre-existing lung disease (P = 0.017) than those without cancer. There were 196 (35%) patients determined to have MAC pulmonary infection, among whom 49 (9%) received directed antibiotics. Those receiving antibiotics had lower body mass index (BMI) (P < 0.0001), more frequent pre-existing lung disease (P = 0.003) and lower cancer rates (P = 0.008) than those not receiving antibiotics. Patients receiving antibiotics were more likely to have cavitary disease (P = 0.001), cough/dyspnea (P = 0.012), hemoptysis (P < 0.001), and constitutional symptoms (P = 0.001).

In concordance with ATS guidelines, hemoptysis, constitutional symptoms, cough/dyspnea and cavitary disease were associated with highest likelihood to treat with antibiotics. The phenotype in cancer patients was quite different than the classic Lady Windermere syndrome. MAC pulmonary infection was treated less often in cancer patients. This study extends beyond the ATS guidelines to examine the potential import of malignancy on the colonization and potential treatment of MAC.