Medullary carcinoma (MC) of the large intestine is a distinct entity that needs to be differentiated from poorly differentiated colorectal carcinoma (PDC). The neoplastic cells of MC are characteristically composed of sheets of uniform medium to large sized cells with amphiphilic cytoplasm, vesicular nuclei and prominent nucleoli, whereas, the neoplastic cells of PDC are typically more pleomorphic then those of MC, however, there are no strict morphological criteria that serve to differentiate these two entities. This is further compounded by the fact that certain morphological criteria for MC are somewhat vague. For example in the World Health Organization monograph (12
) medullary carcinomas are defined as malignant tumors with no glandular structures or features of intestinal differentiation, whereas PDC exhibit at least some gland formation or mucus production (12
). However, many previously reported case series of MC accept some evidence of glandular differentiation such as mucicarmine staining or residual areas of glandular differentiation (2
). The term “large cell carcinoma with minimal differentiation” has also been used to describe what is probably MCs (6
). As there is a considerable difference in prognosis between MC and PDC we attempted to determine whether immunohistochemistry might be used as an adjunct to differentiate between these two entities.
Few studies have attempted to compare the immunohistochemical characteristics of MC directly with those of PDC (2
). Similar to the studies by Wick et al and Sugao et al, we found no difference in the frequency of p53 expression or neuroendocrine differentiation between these two tumors although the latter study found differences in the frequency of NSE expression (2
). In our study, MLH-1 expression was significantly reduced in the MC as opposed to the PDC groups. This finding further supports the contention proposed by Alexander et al that the medullary phenotype of colon cancer is an effective predictor of microsatellite instability (16
Calretinin is a calcium binding protein principally expressed in neurons (17
). Its been shown to be more commonly expressed by PDC tumors as opposed to well-differentiated cancers; however, in the study by Gotzos et al no distinction was made between MC and PDC (8
). Based on our study whereby 73% of MC as opposed to only 12% PDC express calretinin it appears that strong calretinin staining is quite unique to MCs. It is not clear why MC express calretinin, however, in a study using human colonic adenocarcinoma cell lines, Cargnello et al. showed a correlation between calretinin expression and loss of differentiation and proposed a role for calretinin in the maintenance of this undifferentiated state (18
As MC characteristically have an undifferentiated morphological appearance we thought it would also be of interest to determine whether MC express markers typically associated with intestinal differentiation such as: CDX2, CK20, TFF3, MUC1 and MUC2. CDX2, a gene that encodes an intestinal-specific transcription factor expressed in the nuclei of intestinal epithelial cells (19
), is reported to be a sensitive and specific marker of intestinal adenocarcinomas (20
). In a recent study CDX2 was shown to stain a greater proportion of well to moderately differentiated than high-grade tumors (21
). Hinoi et al reported that CDX2 shows a lower percentage of staining in MC compared to well differentiated colorectal carcinomas (6
), suggesting a loss of intestinal differentiation in MC. Our study, the only report which directly compared expression of CDX2 between MC and PDC, found strongly significant decreased expression of CDX2 in MC as opposed to PDC. Although not specific for colorectal neoplasms, CK20 universally stains normal intestinal epithelium and the majority of colonic adenocarcinomas (22
). Here we show that approximately one third of MC express CK20, which was not significantly different from the PDC group.
This is the first study to examine TFF3, MUC1 and MUC2 expression in MC. TFF3 otherwise known as the intestinal trefoil factor is a gene normally expressed in goblet cells of the intestinal epithelium (9
) and is thought to play a role in epithelial restitution (23
). The expression of TFF3 has been shown to be preserved in the human colonic adenocarcinoma sequence (24
), and may be associated with aggressive behavior (23
). MUC1, a non-secretory glycoprotein expressed along the apical membrane of colonic columnar epithelium, is expressed also by colorectal carcinomas and has been shown to behave as a marker for tumor progression (10
). MUC2, considered as the principal secretory intestinal mucin, is expressed by goblet cells (11
), colonic adenomas and adenocarcinomas (26
). The staining pattern for MUC1, MUC2 and TFF3 in MC was diffusely cytoplasmic as opposed to a membranous pattern in normal colonic epithelium suggesting that these tumors are not able to glycosylate and transport these proteins into their original apical regions. However despite its undifferentiated morphology a significant proportion of MC express these three intestinal markers as MUC1, MUC2 and TFF3 staining was seen in 67, 60 and 53% of MC.
An immunohistochemical panel including MLH-1, CDX2, and calretinin would likely be useful in cases were the differential diagnosis of a poorly differentiated colorectal neoplasm includes MC and PDC. In our study a MLH-1 negative, CDX2 negative, calretinin positive phenotype had an 82% positive predictive value for correctly identifying MC. It will be of interest to determine whether calretinin is expressed by tumors with similar phenotypes to that of MC originating from other organs such as the stomach, nasopharynx and breast. If these medullary-like tumors do not express calretinin, then calretinin positivity may be suggestive of colonic origin in biopsies of metastatic disease where the primary is unknown and other markers typically positive in colonic adenocarcinoma (CK20 and CDX2) are negative. Finally, while some markers of intestinal differentiation such as CDX2 showed a low frequency of staining, evidence of intestinal differentiation by MUC1, MUC2 and TFF3 staining was seen in the majority of MC confirming that some degree of intestinal differentiation is preserved in MC.