Introduction
Most Crohn’s disease-associated small bowel carcinomas (CrD-SBCs) show unfavourable outcome due to a highly invasive pattern coupled with advanced stage at diagnosis [
1‐
3]. Attempts to achieve an early diagnosis by the endoscopic screening of Crohn’s disease patients proved relatively ineffective compared with findings reported for early inflammatory bowel disease (IBD)-associated colorectal cancer [
4‐
7]. This relative inability to endoscopically and histologically identify the precursors of CrD-SBC probably depends on the inability of endoscopy to routinely view the small intestine as well as on the limited knowledge of the histogenesis and natural history of CrD-SBCs. Indeed, there is some evidence that apparently non-dysplastic mucosa of cancer-bearing Crohn’s patients shows cancer-mimicking molecular changes [
8,
9]. Therefore, efforts should be made to obtain a better characterization of putative cancer precursor lesions, alternative to or preceding established dysplasia, such as the long-known “pyloric” or “gastric” type metaplasia [
10,
11], the “hyperplastic-like non-conventional type of dysplasia” [
12] or the “ulcer-associated cell lineages (UACL)” [
13,
14], previously reported in Crohn’s disease affected small bowel mucosa.
In a recent study on small bowel cancers, we were impressed by the large prevalence of non-intestinal tumour cell phenotypes among CrD-SBCs, partly mimicking gastric and/or pancreatobiliary duct cells, as well as by the occurrence, within their associated non-tumour mucosa, of focal changes showing the same “metaplastic” cell phenotypes as the cancer tissue itself [
15]. We wondered whether such metaplastic changes may have a role in CrD-SBC histogenesis and progression, also considering previous suggestions concerning CrD-SBC [
11,
16,
17] or IBD-promoted carcinogenesis [
18]. In relation to this and in addition, we also considered the small bowel counterpart of the “non-conventional” low-grade dysplastic lesions, recently characterized among IBD patients with colorectal cancer [
19].
In this study, we analysed the tumour cell phenotype, as well as putative precursor lesions in the background mucosa, of a large cohort of CrD-SBCs, collected and followed through the Small Bowel Cancer Italian Consortium and correlated these data with patients’ clinical outcome. Histologic and immunohistochemical findings in these cases were compared with those obtained in sporadically arising SBCs, in the absence of predisposing chronic immune-inflammatory diseases.
Discussion
In this study, we found that two non-intestinal markers, i.e. CK7 and MUC5AC, were expressed at significantly higher percentages in both tumour tissue and associated mucosa of CrD-SBC cases compared to ordinary no-PID-SBC cases. This finding, in addition to a significant increase among CrD-SBCs of the non-cohesive histotype and a lack of CK7 and MUC5AC expression in histologically normal ileal mucosa, suggests that a distinctive carcinogenic process plays a role in a relevant fraction of CrD-SBC cases. This hypothesis is reinforced by the highly significant association of CK7 expression between tumour tissue and respective mucosa, an association lacking in no-PID-SBC cases, as well as by the occasional finding of direct topographic continuity between CK7 and/or MUC5AC-positive mucosal lesions and the invasive cancers of the same phenotype, which we identified in some CrD-SBC cases. The additional observation that tumour CK7 positivity was an independent adverse prognostic factor points to some mechanism underlying the metaplastic growth which may favour both tumour development and progression.
Metaplastic changes of gastric type, with special reference to MUC6-positive “pyloric” glands, have long been reported in Crohn’s disease intestinal mucosa [
10,
11]. While confirming this finding in non-neoplastic mucosa of CrD-SBCs cases, we found limited expression of MUC6 in corresponding cancer tissue and a lack of MUC6 prognostic influence, two observations rendering unlikely a significant contribution of MUC6-positive pyloric-type differentiation to CrD-SBC natural history. On the other hand, the involvement of the gastric foveolar cell marker MUC5AC is suggested by its high expression in both CrD-SBCs and nearby mucosa and by its association with worse patient outcome, in keeping with previous findings by others in SBC patients as a whole [
31] or in the ampullary [
32] and non-ampullary duodenal cancer patients [
33].
CrD-SBC patient survival analysis highlighted an important prognostic influence of CK7-positive metaplastic phenotype. In particular, we found a significant association between CK7 expression by SBC and worse patient survival, which was confirmed at multivariable analysis inclusive of patient age, stage and histotype. Present findings suggesting a relationship between CK7 expression and CrD-SBC progression fit with previous observations on SBC as a whole [
26] and on colorectal cancers [
34,
35], where poor tumour differentiation, high tumour budding and increased invasive and metastatic potential were frequently observed in CK7-expressing cancers. No information is presently available on possible mechanisms involved in such tumour behaviour. Of interest is our finding of prominent desmoplasia associated with CK7-positive (especially mixed type) invasive cancers, as cancer desmoplasia and/or “mesenchymal” molecular subtype have been linked to worse prognosis in several digestive cancers, including gastric [
36], pancreatic [
37] and intestinal cancers [
23,
25,
38‐
40]. Based on our findings, the MSI hyper-immune subtype, of known better prognostic value among various gastrointestinal cancers, including SBCs, [
22‐
24] appears to be less represented and without prognostic relevance among CrD-SBCs.
In both CrD-SBCs and associated mucosa, metaplastic marker expression was commonly associated with loss of canonical intestinal markers, with special reference to the CDX2 transcription factor. This seems interesting as, in keeping with previous findings on gastrointestinal cancers, including SBCs as a whole [
17,
41,
42], we found that CDX2 predicts improved patient survival. Although in the present CrD-SBC series it failed to remain significant at multivariable analysis due to collinearity with stage and histotype, this survival influence of CDX2 expression should be considered in light of the crucial role played by CDX2 in intestinal epithelium differentiation and metaplastic lineage development. Indeed, it has been recently shown in vitro by Simmini and coworkers [
43] that loss of CDX2 expression alone is enough to transform intestinal stem cells into gastric lineages. Thus, the foci of CDX2 expression loss we found in ileal mucosa of Crohn’s patients might well be a starting point for the metaplastic changes occurring in vivo in this disease, either of gastric type (of pyloric, foveolar or their common precursor lineage) or of non-gastric CK7-expressing type. In this respect, the role of CK7 as a marker of gut foetal, embryonic or pluripotent stem cells [
44‐
46] should also be considered, in addition to its expression by adult epithelia, such as pancreatobiliary ducts. More work on the mechanisms underlying small bowel Crohn-related metaplastic changes is certainly needed; however, their apparent relevance for both origin and progression of associated cancers seems worth additional investigation, also considering the putative role played by CK7 in other gastrointestinal diseases, such as Barrett’s oesophagus [
47,
48], a known metaplastic carcinogenic lesion, and colorectal cancer [
34,
35].
In addition to classic/conventional dysplastic lesions [
1‐
7], several “non-conventional” atypical lesions or growths have been reported to be associated with (and likely precede) cancer development in IBDs of both large and small intestine [
12,
19,
30,
49,
50]. We also found such lesions in the mucosa overlying or adjacent to CrD-SBC; indeed, in seven cases, these were in direct continuity with cancer tissue and sometimes with patterns suggestive of direct transition. Thus, despite their polymorphic histology, incompletely defined diagnostic criteria and substantial lack of frank dysplasia, a role for such atypical, non-conventional lesions in the histogenesis of some CrD-SBCs seems likely.
In conclusion, our fairly large retrospective CrD-SBC series showed important heterogeneity of histologic structure and tumour cell phenotype, also paralleled in part by a polymorphism of mucosal precancerous changes. Among the latter, in addition to classic (conventional) dysplasia, CK7-positive and MUC5AC-positive metaplastic lesions, on one hand, and non-conventional, atypical growths, on the other hand, may have a role in Crohn’s disease-promoted cancer histogenesis. In addition, tumour CK7-positive metaplastic phenotype and non-cohesive histotype were both found to predict CrD-SBC patient adverse prognosis. These findings, besides suggesting a distinctive CrD-SBC natural history, are worth considering in future prospective and endoscopic/bioptic studies aiming to gain diagnosis of early tumourigenic lesions, as well as in attempts to provide more appropriate and patient-personalized treatments [
22,
42,
51].
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