The positive rate of CD9 expression from the cases that had well-differentiated adenocarcinoma, with the largest tumor diameter <2 cm, and without lymph node metastasis, and that did not invade the surrounding tissue was significantly higher than that of CD9 expression from the cases that had poorly differentiated adenocarcinoma, with the largest tumor diameter ≥2 cm, lymph node metastasis, and which invaded the surrounding tissues (P <0.05 or P <0.01). Here, CD9 is linked to adenocarcinoma.