Given elderly patients’ frequent intolerance of the multidrug regimen needed to treat Mycobacterium aviumcomplex (MAC) infections, some patients with solid tumors may do better and survive for prolonged periods with observation compared with pharmacotherapy. Watchful clinical and radiographic monitoring may alert physicians if the infection progresses to a point of requiring treatment.
Reporting at the 47th annual meeting of the Infectious Diseases Society of America, researchers from The M. D. Anderson Cancer Center in Houston, Texas, characterized the natural history of MAC infection in cancer patients who were intolerant of antimycobacterial therapy or elected not to receive it. Their study was a retrospective review of the medical records of 10 such patients at their institution between 2004 and 2009. All had laboratory-confirmed MAC infection.
Patients had a median age of 70.8 years, 90% were women, and all were afebrile and asymptomatic for MAC. Four were receiving antineoplastic therapy, five elected not to receive therapy for MAC, and an additional three discontinued standard triple-drug therapy (ethambutol and a macrolide plus either rifampin or moxifloxacin) at 3 to 12 weeks because of intolerance. Two patients completed 18 months of therapy but had persistent positive cultures and radiographic changes. All 10 patients were followed for a median of 28 months (range, 9-57 months) without MAC therapy.
Coralia Mihu, MD, an assistant professor at the cancer center, reported that all the patients remained minimally symptomatic or asymptomatic, although there was some waxing and waning of pulmonary opacities in all 10 patients. None developed progressive infection of the lung requiring therapy.
Mihu told The Oncology Pharmacist that active chemotherapy for cancer in four patients did not appear to put them at higher risk for worsening of MAC infection. She noted that her findings are important because of the many patients with MAC infection, a group that tends to be older, on polypharmacy, and often has comorbidities. "Therefore, three drugs added on their already complicated medication regimen makes things worse in terms of tolerability," she said. Also, MAC therapy may require 12 to 18 months.
In the absence of MAC treatment, Mihu advised following asymptomatic patients closely with frequent chest imaging, and said "[MAC] is worth treating in patients who do have clinical signs of worsening infection...like low-grade fevers or productive cough, which our patients did not."