Mesenchymal stem cell (MSC)-based therapies have been considered an attractive approach for treating Huntington's disease (HD). However, due to the pulmonary first-passage effect associated with intravenous infusion (the most commonly used route of MSC administration), there is a rising concern that the cells could be entrapped in the lungs and grafted (homing) into preexisting lung cancer. Herein, we report the case of a patient with HD enrolled in a cell therapy phase I clinical trial for HD treatment having a preexisting pulmonary nodule. The nodule was found at the trial screening. The patient was referred to a pulmonologist who considered the nodule non-cancer and authorized enrollment. The patient received four intravenous administrations of human immature dental pulp stem cells (hIDPSCs) at the dose of 1 × 106 cells/kg of body weight within 2 years. One month after the last dose, a computerized tomography scan showed nodule growth. A bronchoscopy biopsy showed primary lung adenocarcinoma. The neoplasm was surgically excised (lung superior right lobectomy). The patient is cured of the neoplasm. The tumor was sectioned into six fragments, which were subjected to RNA-seq. The transcriptome of each tumor section was compared with the transcriptome of infused hIDPSCs using two statistical approaches: principal component analysis and NOIseq. Both results demonstrated a linear distance between the hIDPSCs and the lung adenocarcinoma. These results suggest that the infused hIDPSCs neither home nor graft within the pulmonary nodule.