Background/aims: In TNM classification, carcinoma that has invaded the muscularis propria (mp) and cancer that has invaded the subserosa are both categorized as T2 cancer. However, some mp gastric cancer patients have a good postoperative course, similar to that of early gastric cancer patients. We performed a retrospective analysis of 74 patients with mp gastric cancer, based on the depth of mp invasion.
Methodology: The clinicopathologic features of 74 cases of gastric cancer invading the mp (but no further) were subdivided according to depth of invasion, retrospectively reviewed and compared with surgical features of 165 patients with gastric cancer invading the submucosa (sm gastric cancer). For each tumor, we evaluated the degree of tumor invasion in the mp layer at a magnification of x100, using the section that showed the greatest extent of invasion. The patients were classified into 2 groups: mp1, tumor was limited to the first of the 3 mp layers; mp2, tumor had expanded beyond the first layer.
Results: Of the 74 mp gastric cancer patients, 30 were classified as mp1 and 44 were classified as mp2. Patients with mp1 gastric cancer had significantly more macroscopic signs of early gastric cancer, a lower frequency of lymph node metastasis, and a higher rate of operative cure than patients with mp2 gastric cancer. The incidence of lymph node metastasis among mp1 gastric cancer patients was almost equal to that of the 165 sm gastric cancer patients. The 5-year survival rate of mp1 patients was significantly better than that of mp2 patients (p<0.05), but was similar to that of the 165 sm gastric cancer patients (84%) (p<0.05).
Conclusions: There were clear differences in clinical features between the mp1 and mp2 gastric cancer patients. Subdivision of mp gastric cancer according to depth of invasion may enable more precise prognosis and treatment of mp gastric cancer patients. The clinicopathological findings and surgical outcome of the mp1 patients were similar to those of the sm gastric cancer patients. Thus, mp1 patients may require treatment that is similar to treatment administered to patients with early gastric cancer.