Interpretation of a heterogeneous radiological response as tumor heterogeneity or a non-tumor diagnosis: A case report.

Heterogeneous radiological responses (HRRs) among tumor lesions are usually observed following chemotherapy or radiation treatment in cancer patients. When HRR is observed after chemotherapy or radiation treatment, a change in anticancer treatment is recommended due to the clinically high suspicion of resistance in the majority of cases. The present study reports the case report of a patient with limited-stage small cell lung cancer, diagnosed by bronchoscopy, who received concurrent chemoradiation therapy. Upon response evaluation, the majority of lesions irradiated had nearly completely disappeared following treatment, but one lesion had apparently increased in size. For histological confirmation, a percutaneous needle biopsy for the lesion was performed, however, non-specific necrosis was found and the results were inconclusive for the differentiation of other causes from tumor necrosis. Several acid-fast bacilli were identified on Ziehl-Neelsen staining for the differential diagnosis. This case suggests that a non-tumor diagnosis should be considered when HRR presents after treatment that is expected to result in a higher response rate, particularly in tuberculosis endemic areas.