Significant positive correlation between MUC4/Y mRNA expression level and TNM stage, MUC4 mRNA expression level, and survival in PDAC. (A) Schematic representation of the design strategy for specific primers and TaqMan probe in MUC4/Y gene detection based on the difference between the exon sequences of MUC4/Y (NCBI Reference Sequence: NM_004532.5) and FL-MUC4 (NCBI Reference Sequence: NM_018406.6). The TaqMan probe sequence lies in the exon 1–exon 3 junction; as exon 2 is absent, it detects MUC4/Y expression rather than other MUC4 types encoding the exon 1–exon 2 junction, or MUC4/X (NCBI Reference Sequence: NM_138297.4), which encodes the exon 1–exon 4 junction because it lacks the coding exons 2 and 3. Primers and TaqMan probe are underlined. (B) Comparison of MUC4/Y mRNA expression at different TNM stages. Scatter dot plots were drawn from the minimum extending to the maximum; the center horizontal line denotes the sample median. *P <0.05, **P ≤0.01, ***P ≤0.001. (C) Positive correlation between MUC4/Y and MUC4 mRNA expression (R
2 = 0.430, P <0.001) and curve fitting. Regression equations were Y = 6.553 + 0.3212 × X + 0.02719 × X/2–0.00033333 × X/3 (cubic), Y =6.522 + 0.3514 × X + 0.02102 × X/2 (quadratic), and Y =5.915 + 0.6127 × X (straight line). According to the correlation coefficient value, the cubic or quadratic curve model was the better model. Ct, threshold cycle value. (D) Kaplan–Meier survival curves of PDAC patients according to MUC4/Y mRNA expression status. The P-value was calculated using the log-rank test.