Some gastric cancer patients in whom the cancer has infiltrated up to the muscularis propria (mp) have a good postoperative course similar to that of early gastric cancer (EGC) patients (this does not match the general classification of gastric cancer). Therefore, we performed a retrospective analysis of 125 patients with mp gastric cancer based on the degree of mp invasion.

The clinicopathologic features of 125 cases of mp gastric cancer were subdivided according to depth of invasion, and were retrospectively reviewed and compared with the surgical features of 222 patients with gastric cancer invading the submucosa (sm). For each tumor, using the section that showed the greatest extent of invasion, we evaluated the degree of tumor invasion into the mp layer at a magnification of x100. The patients were classified into 2 groups: mp1, the tumor was limited to the first of the 3 mp layers, and mp2, the tumor had expanded beyond the first layer.

Patients with mp1 (n=50) had a significantly lower incidence of lymph node metastasis, and a smaller tumor size than patients with mp2 (n=75)(P=0.01 and P=0.029, respectively). The 5-year survival rate of mp1 patients was significantly better than that of mp2 patients (95.3% vs. 77.6%, P=0.0282), but was similar to that (91.2%) of the 222 sm patients. The 5-year survival rate of mp patients without lymph node metastasis (n=55) was significantly better than that of those with lymph node metastasis (n=70)(93.3% vs. 78.2%, P=0.0192). Patients with mp1 had a significantly higher incidence of lymph node metastasis (42.5% vs 23%, P=0.006) than patients with sm.

There were clear differences in clinical features between the mp1 and the mp2 patients. Subdivision of mp gastric cancer according to the depth of invasion may enable a more precise prognosis and a more pertinent treatment plan for mp patients. In particular, as the clinicopathological findings and surgical outcomes for mp1 patients were akin to those of the sm patients, mp1 patients may require treatment analogous to that administered to patients with sm gastric cancer.