a 49-year - old , nonsmoking female had been treated for aml with one course of induction chemotherapy with the use of daunorubicin and cytosine arabinoside ( ara - c ) . after relapse of aml , the patient was treated with 10 mg / m iv mitoxantrone daily for six days and 3 g / m iv ara - c , daily for six days . on day six , flu - like symptoms including fever and cough developed after completion of the chemotherapy . on examination , the patient had an elevated temperature ( 38.5  ) and tachypnea . the results of arterial blood gas analysis in room air were as follows : pao2 92 mmhg , paco2 30 mmhg and ph , 7.37 . the results of a laboratory evaluation were as follows : hemoglobin level , 104 g / l ; platelet count , 140,000/l ; white blood cell count , 11,100/l . the level of c - reactive protein and the erythrocyte sedimentation rate did not increase . fiberoptic bronchoscopy showed patent airways and the bronchoalveolar lavage ( bal ) fluid was non - diagnostic . culture and microscopy of sputum and bal materials were negative for fungi , bacteria , acid - fast bacilli , pneumocystis carinii and cytomegalovirus . empirical antibiotic therapy was initiated for a case of presumed pneumonia . over the next few days , fever and cough persisted in spite of the antibiotic treatment . on day 11 , twenty hours later , a chest computed tomography ( ct ) scan confirmed the presence of numerous discrete 1-mm to 5-mm nodules throughout the lungs ( fig . 1b , c ) . due to the poor response to the antibiotic treatment and the questionable diagnosis of pulmonary metastases , a video - assisted thoracoscopic lung biopsy with wedge resection of the posterior segment of the right upper lobe was performed on day 13 . histopathological analysis revealed that polypoid granulation tissue was filling the air spaces and foamy macrophages and inflammatory cells with interstitial pneumonia and air - space fibrosis were present , consistent with cop ( fig . 1d , e ) . dramatic improvement of the clinical symptoms and radiographic abnormalities was noted after two weeks of appropriate steroid treatment ( fig . 1f ) , and the lesions were almost completely resolved after three weeks ( fig . 1 g ) . at a follow - up visit one month after discharge , the patient remained asymptomatic and chest radiograph showed a stable appearance . cryptogenic organizing pneumonia is a distinct clinicopathological entity characterized by a subacute illness with shortness of breath , fever , cough , malaise and patchy peripheral air - space infiltrates as depicted on chest radiographs ( 1 ) . the disease is defined histopathologically as granulation tissue plugs within the lumina of small airways , alveolar ducts and alveoli ( 2 ) . most cases are idiopathic and may be secondary to infections , a hematological malignancy , connective tissue disorders , drug administration , exposure to radiation or bone marrow or lung transplantation ( 2 , 3 ) . cryptogenic organizing pneumonia has a variable radiologic appearance and is usually characterized by unilateral or bilateral areas of patchy air - space consolidation with a subpleural and peribronchial distribution ( 1 , 2 ) . in a review of 14 patients with cop , mller and colleagues ( 4 ) found no single finding or combination of findings that could be considered diagnostic of this disease . the presentation of a patient with diffuse discrete 1-mm to 5-mm pulmonary nodules associated with cop is uncommon . correlation of the high - resolution ct abnormalities with the findings on video - assisted thoracoscopic biopsy suggest that the nodules seen on ct corresponded to localized areas of organizing pneumonia around the bronchiolitis obliterans . this pattern of lesions is separated from other involved bronchioles by a zone of relatively normal parenchyma , explaining the nodular appearance . the findings differ from the patchy or confluent nodular infiltrations usually associated with cop ( 5 , 6 ) . the clinical presentation in this case differs from that of neoplastic diseases , however , due to the rapid progression to diffuse nodules over a few days . furthermore , multiple nodules are not always a sign of malignant disease , and benign lesions such as tuberculosis and fungal and parasitic infections should be considered in the differential diagnosis . definitive differentiation of cop from infectious diseases by imaging studies , however , is usually not possible . the absence of microorganisms in cultures of blood , sputum , and bal fluid and the failure of empirical antibiotic treatment ruled out active infection at the onset of pulmonary symptoms in our patient . the factors responsible for cop in this case remain unclear but may include a direct immunologic reaction resulting from a possible subclinical viral infection , a toxic reaction to the chemotherapeutic agents and underlying hematological disease . however , whatever the etiology of cop in this case , the clinical symptoms and pulmonary lesions dramatically improved as the patient was responsive to steroid therapy . further , early diagnosis prevented the patient from having rapidly progressive cop that is a deadly form of the disease and can occur in a small percentage of patients ( 7 ) . as pointed out in previous studies , benign pulmonary nodules in patients with an underlying malignancy have occasionally been seen in the setting of allogeneic bone marrow transplantation ( 8) or in chemotherapeutic drug toxicity ( 9 ) . in our patient , the question of drug - induced cop arises as bone marrow transplantation was not performed and the clinical and radiological manifestations of pulmonary lesions developed after chemotherapy . our patient , however , was not given bleomycin , which has been associated with nodular cop mimicking pulmonary metastases ( 10 ) . the association between the administration of high - dose intravenous ara - c and lung toxicity is well recognized , and battistini et al . ( 11 ) reported the development of cop in three children with acute leukemia who received a combination of high - dose ara - c and anthracyclines , which is similar to the regimen that was followed by our patient . therefore , although undetectable infectious agents may be etiologic factors , chemotherapeutic toxicity can be presumed . in conclusion , our patient had an unusual radiological pattern of diffuse discrete pulmonary nodules associated with cop that mimicked pulmonary metastases . the development of new pulmonary symptoms accompanied by a radiological manifestation of diffuse pulmonary nodules in cancer patients during chemotherapy should prompt consideration of this diagnosis so that appropriate steroid treatment can be initiated .