An 18F-FDG PET/CT showed slight accumulation (SUVmax = 0.90) (Figure 3C). Despite the low SUVmax value, a CT-guided biopsy was performed due to the elevated plasma ProGRP level. Pathological examination confirmed a pulmonary carcinoid, leading to a diagnosis of clinical stage IA2 (T1bN0M0). The patient subsequently underwent radical treatment, including resection of the left lingual region and lymph node dissection (ND1). Postoperative pathology confirmed the tumor as a typical carcinoid (Figure 4). Here, GRP is linked to neoplasm.