New lung mass in a patient with granulomatosis with polyangiitis.

Granulomatosis with polyangiitis (GPA) is a potentially lethal ANCA-associated small-vessel vasculitis characterized by a typical triad of upper respiratory tract, lung, and kidney involvement. Lung involvement in GPA occurs in 25-80% of cases. The most common radiographic and computed tomography (CT) abnormalities of pulmonary GPA are lung nodules and masses, very often multiple and with cavitation. As there are various clinical presentations, the diagnosis of GPA can be challenging, and the illness is difficult to distinguish from other diseases such as infection or malignancy. Following the improved survival rates in patients with GPA, there is accumulating evidence to suggest an increased occurrence of different types of cancer. Exposure to cyclophosphamide seems to be one of its main causes. We present the case of a patient with chronic GPA who was hospitalized owing to a new infiltrate in the lung, suggesting relapse of the disease, and finally diagnosed with small cell lung cancer. Data regarding lung cancer in GPA patients are limited. While there are some case reports and short case series in the literature, there are no detailed data regarding an association between CYC exposure and lung cancer development in vasculitis. It is necessary to consider the causes of pulmonary masses other than a GPA relapse. Bronchoscopy with biopsy and histopathological examination are crucial in proper differential diagnosis. GPA patients require long-term follow-up to monitor for the development of complications during treatment.