Objective Our previous studies have demonstrated a high percentage of mucinous carcinomas in colorectal cancer associated with schistosomiasis (CCS). This is a further study to explore whether there are special immunohistochemical and histochemical characters in CCS or its subtypes.Methods A comparative study was carried out in benign and malignant colorectal tissues with and without schistosomiasis. The study included a quantitative determination of peanut lectin (PNA)-binding sites and proliferating cell nuclear antigen (PCNA) expression and histochemical detection of mucin changes. These methods have often been applied to the study of colorectal cancer but have not been recorded in the study of CCS. 133 cases were investigated, of which 70 cases were of CCS and 63 cases were of colorectal carcinoma without schistosomiasis (CC). The two groups were subdivided into mucin-containing (MC) and non-mucin-containing (NMC) subtypes.Results Non-tumorous mucosa of the CCS group showed 47% PNA positive cases, significantly higher than 25% in the CC group (P<0.01). The difference was mainly found in MC subtype of CCS. 65% of non-tumorous mucosa adjacent to MC of the CCS group exhibited PNA binding, and in MC of the CC group, only 31% (P<0.05). Moreover, the non-tumorous mucosa in the cases of MC of the CCS group also showed a high percentage of sialo-mucin-predominant secretion (69% vs 38% in MC of the CC group, P<0.05). Consistently, the presence of PNA-binding sites in MC tumors of the CCS group was increased, compared with that in the same subtype in the CC group (65% and 31%, respectively, of strong positivity for PNA, P<0.05). However, no differences in expression of PNA and mucin changes were demonstrated in the surrounding mucosa and tumorous tissues of NMC between CCS and CC. The expression of PCNA was not different between CCS and CC and their subtypes.Conclusions Because PNA has an ability to bind to specific sugar molecules that have been proved to be closely related to early malignant change in colonic epithelia, and a predominance of sialomucins (50% or more) is regarded as abnormal mucin patt valuable in identifying early development of epithelial dysplasia and pre-malignant changes, the high frequency of PNA-binding sites in non-tumorous and tumorous tissues of the CCS group and its MC subtype and the increase of sialomucins in non-tumorous mucosa of MC of the CCS group could be considered as a stronger tendency of malignant transformation in the colorectal epithelia influenced by schistosomiasis. If these malignant changes in the schistosomal colon are postulated to result in MC subtype tumors, it could explain the significantly high proportion of MC in the CCS group (P<0.05). With a review of current knowledge on the association of schistosomiasis and colorectal cancer, we propose that schistosomiasis japonica might have a close relation with mucin-containing types of colorectal cancer.