Pulmonary cryptococcosis mimicking metastatic progression despite systemic disease stability in advanced colon cancer: A case report and literature review.

rationaleIn patients with advanced cancer, newly detected pulmonary nodules are often interpreted as metastatic progression. The distinctive feature of this case was the appearance of multiple new lung nodules during otherwise controlled systemic disease: the primary colonic lesion and hepatic metastases remained stable while tumor marker levels declined. This radiologic-clinical discordance prompted reconsideration of metastatic progression and broadened the differential diagnosis. PATIENT CONCERNS: A patient with advanced colon cancer, who was undergoing systemic chemotherapy and had otherwise stable disease, was found to have developed new pulmonary nodules on routine surveillance imaging. The patient was entirely asymptomatic from a respiratory standpoint. The primary clinical concern was the discordance between the radiologically suspicious findings and the patient's overall stable clinical condition. DIAGNOSES: The initial radiologic impression favored pulmonary metastases. However, multidisciplinary review recognized the discordance between the new lung lesions and the otherwise stable systemic disease and raised concern for an opportunistic infection. Serum (1,3)-β-D-glucan and qualitative cryptococcal capsular polysaccharide antigen tests were positive, supporting a diagnosis of pulmonary cryptococcosis.

interventionsAfter cerebrospinal fluid evaluation excluded central nervous system involvement, fluconazole 400 mg once daily was initiated. The anticancer strategy was not escalated on the basis of the pulmonary findings alone. OUTCOMES: Follow-up chest computed tomography demonstrated marked regression of the pulmonary nodules. LESSONS: When new pulmonary lesions arise despite stability or response at established tumor sites, apparent radiologic progression should not automatically be equated with oncologic progression. Integrating the longitudinal treatment response, tumor marker trends, clinical symptoms, imaging features, and targeted infectious testing can prevent unnecessary changes in cancer therapy and may avoid invasive procedures when a sufficiently supported alternative diagnosis is available.