P72 | Luckily, things are not always as they seem!

Background: Alectinib, a second-generation ALK inhibitor, plays a crucial role in the treatment of lung cancer. The use of molecular-targeted drugs has heightened the occurrence and expanded the range of lung toxicity, specifically drug-related pneumonitis (DRP).Description: In December, a 58-year-old patient diagnosed with stage IV lung adenocarcinoma was admitted to our Medicine Department due to a fever and acute respiratory failure. He was currently treated with Alectinib and in good clinical remission. The chest CT scan revealed unclear submantle multiple consolidations, while the lab findings showed normal C-reactive protein levels and white blood cell count. A panel of tests for pulmonary pathogens was asked. The treatment started with methylprednisolone, low-flow oxygen, and antimicrobial therapy with azithromycin and ceftriaxone. Alectinib was ceased and a DRP was supposed. In 7 days, dyspnea subsided, and the need for supplemental oxygen was discontinued. The laboratory tests showed IgM and IgG for Mycoplasma pneumoniae. Thus, as the patient was asymptomatic, he was discharged and able to resume therapy with alectinib.Conclusions: The symptoms of drug-related pneumonitis are nonspecific, as are the chest CT findings, often manifesting as interstitial pneumonia. Distinguishing pulmonary infiltrates related to DRP can be challenging. Mostly, suspicion of DRP arises only after thorough exclusion of other potential causes. In this specific case, the diagnosis of Mycoplasma pneumoniae infection ruled out DRP, allowing the patient to keep on with his effective therapy.