Abstract Purpose Pancreatic cancer (PC) is the most lethal cancer. The prognosis of small PC (tumor smaller than 20 mm) is better than that of larger PC tumors, indicating the importance of detecting early-stage PC for patient outcome. The aim of this study was to elucidate the molecular features in small PC (≤ 20 mm). Methods This study included 79 PC tumors (≤ 20 mm in pathological examination) resected between 2004 and 2022. c-Myc, Caveolin-1, Smad4, and Thrombospondin-1 were examined by immunostaining. These molecular alterations were compared in PC patients with tumor size ≤10 mm (n = 11) (14%) and 10 mm < tumor size ≤20 mm (n = 68) (86%). Mutation analyses of KRAS, PIK3CA, and BRAF were performed by pyrosequencing in 22 PCs. Results PC with 10 mm < tumor size ≤20 mm showed significantly worse overall survival and disease-free survival than PC with tumor size <10 mm (P = 0.024 and P = 0.028). Tumor c-Myc and stromal Caveolin-1 expressions were significantly increased in tumors larger than 10 mm (P = 0.02 and P = 0.04). c-Myc and Caveolin-1 expressions were associated with poor disease-free survival and overall survival. KRAS, PIK3CA, and BRAF mutation status did not differ between the two groups. Conclusions Tumor c-Myc and stromal Caveolin-1 overexpressions were detected in tumors larger than 10 mm. Their overexpressions were associated with worse prognosis even in small PC. These molecular alterations in small PC may be a clue for the detection of early-stage PC.
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