Mycobacterium Avium-Complex Infections in Elderly Cancer Patients May Not Require Treatment

Daniel M. Keller, PhD

November 11, 2009

November 11, 2009 (Philadelphia, Pennsylvania) — A subset of patients with solid organ malignancies and pulmonary Mycobacterium avium–complex (MAC) infections might fare worse if the infection is treated. These patients, who are often intolerant of the 3-drug regimen, can be successfully followed with close clinical and radiographic monitoring and may survive for prolonged periods without treatment of the infection.

To characterize the natural history of pulmonary MAC infection in cancer patients who were intolerant of antimycobacterial therapy or elected not to receive it, researchers at the University of Texas M.D. Anderson Cancer Center in Houston did a retrospective review and analysis 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 female, and all were afebrile and asymptomatic for MAC. Four patients were receiving antineoplastic therapy. Five of the 10 patients elected not to receive therapy for MAC, and an additional 3 patients discontinued standard triple-drug therapy at 3 to 12 weeks because of intolerance. Two patients completed 18 months of therapy but had persistent positive cultures and radiographic changes. The 10 patients were followed for a median of 28 months (range, 9 to 57 months) without MAC therapy. Triple-drug therapy consisted of ethambutol and a macrolide plus either rifampin or moxifloxacin.

In a poster presentation here at the Infectious Diseases Society of America 47th Annual Meeting, Coralia Mihu, MD, an assistant professor at M.D. Anderson Cancer Center, reported that all the patients remained minimally symptomatic or asymptomatic without antimycobacterial therapy, although there was some waxing and waning of pulmonary opacities in all 10 patients. None developed progressive infection of the lung that required treatment.

Dr. Mihu told Medscape Infectious Diseases that although 4 of the patients were receiving active chemotherapy for their malignancies, "this did not appear to put them at higher risk for worsening of MAC infection."

Even though the sample size was limited, she noted the importance of her observations. "In real life, there are a lot of patients with MAC infection, and most of these patients tend to be old and to be on polypharmacy," she said. "Therefore, 3 drugs added to their already complicated medication regimen makes things worse in terms of tolerability." Treating cancer patients for MAC might be additionally difficult because of advanced patient age, duration of therapy (12 to 18 months), and comorbidities, including their underlying malignancies.

Dr. Mihu advised that just because a patient has active cancer and might be undergoing chemotherapy does not automatically indicate that he/she needs to be treated for MAC, especially if the patient is asymptomatic. This advice is especially pertinent if a patient is seen by healthcare professionals and receives chest imaging frequently so that the course of the infection can be followed closely. But "it is worth treating in patients who do have clinical signs of worsening infection . . . like low-grade fevers, productive cough, which our patients did not," she said.

Paul Riska, MD, attending physician in infectious disease at Montefiore Medical Center in the Bronx, New York, told Medscape Infectious Diseases that some patients are similar to the ones in Dr. Mihu's study, but others have more aggressive disease and require treatment. "There would be more systemic symptoms, [such as] fever, weight loss, high inflammatory markers in the blood," he explained. "Many of these people are assumed to have TB [tuberculosis] and are treated for TB. The lesson is that not everything that looks like TB is TB, and MAC needs to be considered because it often can mimic TB."

MAC cultures can also mask a concomitant TB infection. "MAC grows faster and sometimes can overwhelm TB in dual infections," Dr. Riska cautioned.

The study did not receive any outside funding. Dr. Mihu and Dr. Riska have disclosed no relevant financial relationships.

Infectious Diseases Society of America (IDSA) 47th Annual Meeting: Abstract 1019. Presented October 31, 2009.