Mucin phenotype is a classification based on the mucin markers expression mode. After the year of 2000, the mucin phenotypes of gastric and intestinal were analyzed by IHC(15).The mucin markers of MUC5AC, MUC6, MUC2 and CD10 are considered necessary, though there is no consensus on the amount of markers which should be used to define a mucin phenotype, or the percentage of tumor cells must be stained(6–8,11,15,18). MUC5AC is a secreted mucin expressed in the surface mucous epithelium of normal gastric mucosa. High expression of MUC6 is observed in fundic neck mucous cells and pyloric glands of gastric mucosa. CD10 is a marker for the brush border on the luminal surface of small intestinal. In the normal adult intestine, MUC2 expression is observed in the perinuclear areas of goblet cells.
We showed the expression of MUC5AC, MUC6, MUC2 and CD10 demonstrated in 167 (64.98%), 187 (72.76%), 164 (63.81%), 112 (43.58%) of the 257 EGCs. In the previous researches, the expression of MUC5AC, MUC6, MUC2 and CD10 in GCs was 55.1%~67.5%, 44.9%~64%, 35.4%~49.3% and 20.6%~20.9% respectively[19, 20]. For EGCs, the expression of each mucin marker was 68.75%~96.8%, 19.6%~71.58%, 25%~62.10%, 0%~79% respectively(6,11,21).
Based on the combinations of expression of those markers, the 257 EGCs were classified into G-type (21%,54/257), GI-type (56%,144/257), I-type (20%,51/257) and N-type(3%,8/257). The incidence of each micin phenotype in previous reports have been showed to be 15%~41.1%, 20.3%~60.1%, 18.5%~46.6%, 3.7%~31.6% in advanced GCs(3,13–14), and 7.9%~36.8%, 18.8%~41.2%, 15.4%~55.56%, 0%~11.1% in early stage GCs(7,11,19–22,24–26 )respectively. Our data was consistent with them. As we notice, the reported expression ranges vary greatly among different investigators, different markers, antibodies and case groups may play a role in it. Koyama et al have reported the incidence of G-type was 19.3%(27), which was similar to ours (21%), but in his report, the incidence of I-type was much higher the G-type(43.8% vs. 19.3%), so as Fabio et al.(11). While Tajima et al.(22) reported an opposite result, in their study G-type was much higher than I-type (36.8% vs. 15.4%). In our research, the incidence of G-type is almost as same as I-type (21% vs. 20%). All in all, in our data, much more than half of these cases showed G- and GI-G type (61.09%,157/257), which is much higher than I- and GI-I type(36.96%,95/257), as a previous report revealed that almost all the intramucosal GC cases showed the gastric phenotype, including GI phenotype(28).
The relationship between mucin phenotypes and clinicopathological features was investigated. We found the histology classification (both the JGCA and WHO classification) were closely related with mucin phenotype. The I-type had a higher proportion than G-, GI- and N-type (100.0% vs.79.7%, 93.1%, 87.5%, P = 0.027). The G-type was correlated significantly with the mixed type (with poorly differentiated/papillary carcinoma) histologically. Our data showed the proportion of G-type turned greater during the transition from solely differentiated type to mixed type carcinoma. Mixed type carcinoma in early stage more frequently expressed G-type mucin, and the G-type tumors were associated with a higher rate of undifferentiated-type as compared with the I-type tumors(7,22).
While there were no significant differences between mucin phenotypes and other parameters, including gender, age, margin, color, tumor size, gross type, depth of invasion, lymphovascular invasion (P༞0.05). These results perfectly shared the same viewpoint with some researchers(22,25,29), there was no clear correlation between phenotypes and clinicopathologic characteristics, including sex, age, tumor size, location, macroscopic features, lymphatic or venous invasion, or lymph node metastases in the case of the differentiated type(22,25,29). While Koseki et al.(7) and Oya et al.(30) have reported the incidence of lymphatic invasion, venous invasion and lymph node metastasis in gastric phenotype carcinomas was significantly more frequent than that in intestinal phenotype carcinomas. In addition, G-type GCs had a correlation with some distinguished macroscopic features: the smaller tumor diameter(28), the discolored surface and non-wavy tumor margins(31,32). G-type differentiated adenocarcinomas showed depressed type, indistinct margins and monotonous color tone across the mucosal layer, whereas I-type had an elevated, distinct margin and a red mucosa(3,33,34). The discrepancy of these results may have been due to heterogeneous components which contained poorly differentiated adenocarcinoma(29).
Intestinal metaplasia has been frequently observed surrounding the GC, especially differentiated adenocarcinomas. IM had a malignant potential and has been regareded as a precursor of gastric neoplasms. According to Laurén, The intestinal type adenocarcinoma preceded by metaplastic changes, while the diffuse type adenocarcinoma arised in non-IM gastric mucosa(2). In the current study, the backgroud mucosa IM was observed in 79.9% cases (G-,GI- and I-type) and 87.0% in G-type. 25.5% cases of I-type arised from the normal mucosa without IM. IM did not significantly differ among mucin phenotypes (P༞0.05). But incomplete and complete IM were significantly differed in different mucin phenotypes (P = 0.004, P = 0,018). There were 77.78% (42/54) G-type and 70.6% (36/51) I-type appeared complete IM, which was higher than GI-type (83/114,57.6%). The expression of incomplete IM in GI-type was higher than that of G- and I-type (21.5%vs. 9.3% vs. 3.9%). Our results demonstrated a remarkable difference between mucin phenotypes and the background mucosa. Similar results have been repoted by Kabashima et al.(36)and Matsuoka(37). The mucin phenotype of the carcinoma was independent of mucin phenotypic changes in the surrounding mucosa, they might perform individual intestinalization. G-type might imitate the surrounding mucosa, the carcinomas and the background mucosa had an unstable status, then commonly possess the hybrid phenotype of the stomach and the small intestine(36,37).
Mucin phenotypes can indicate biological behavior in GCs. G-type GCs got increased potential for invasion and metastasis: infiltrating deeper layers or more surrounding structures, higher rate of lymph node metastasis, and poorer prognosis(3,12,18,21). Even, the differentiated adenocarcinoma with G-type had a similar outcome, focused on the prognosis, with undifferentiated adenocarcinoma(7–10). In our research, six patients received additional gastrectomy, and there was no residual tumor or lymph node metastasis. All cases were under close follow-up, neither recurrence nor metastasis were detected. The mixed type (mixed with poorly differentiated or papillary adenocarcinoma) were mainly of G-type, which was significantly higher than that of purely differentiated tubular adenocarcinoma (P < 0.05), and the depth of infiltration was deeper (P < 0.05). G-type had the highest portion (11/54,20.37%) with poorly differentiated/undifferentiated components, and almost all of them (19/22,86.36%) expressed G- and GI-G type. The mixed type may represent a progressive loss of glandular structure during its progression from mucosal to advanced stage, and those with submucosal invasive was a risk factor for lymph node metastatsis.(7,22,38) Differentiated GC with G-type often changed histologically into signet ring-cell carcinoma or poorly differentiated adenocarcinoma. Those imply the fact of more aggressive biological behavior and poorer prognosis.