AIM: To characterize clinicopathological and familial features of early-onset colorectal cancer (CRC) and compare features of tumors with and without microsatellite instability (MSI).

METHODS: Forty-five patients with CRC aged 45 or younger were included in the study. Clinical information, a three-generation family history, and tumor samples were obtained. MSI status was analyzed and mismatch repair genes were examined in the MSI families. Tumors were included in a tissue microarray and an immunohistochemical study was carried out with a panel of selected antibodies.

RESULTS: Early onset CRC is characterized by advanced stage at diagnosis, right colon location, low-grade of differentiation, mucin production, and presence of polyps. Hereditary forms represent at least 21% of cases. Eighty-one percent of patients who died during follow-up showed a lack of expression of cyclin E, which could be a marker of poor prognosis. β-catenin expression was normal in a high percentage of tumors.

CONCLUSION: Early-onset CRC has an important familial component, with a high proportion of tumors showing microsatellite stable. Cyclin E might be a poor prognosis factor.

The prevalence of colorectal cancer (CRC) has been increasing during recent years. In 2004, it had the second highest incidence of all cancers and was the second most common cause of cancer-related death in the European Union[1]. Early onset CRC is infrequent, with an incidence of 2%-8% of all CRCs. In the United States, between 1992 and 2005, the incidence of CRC in young individuals (ages 20-49 years) increased at a rate of 1.5% per year in men and 1.6% per year in women[2].

Early onset of cancer is an indicator that a hereditary component is more likely. The most frequent hereditary form of CRC is Lynch syndrome. It is estimated to represent about 2%-5% of all CRCs, and is characterized by the development of CRC (and other types of cancer) at a mean age of 43 years[3-6]. Its molecular basis is a DNA mismatch repair (MMR) gene defect, which leads to changes in the length of repetitive DNA sequences, known as microsatellite instability (MSI).

The proportion of MSI tumors found in young patients varies between 19.7% and 41%, depending on the age of onset[7-9]. On the other hand, Lynch syndrome is estimated to cause about 1/3 of the CRC cases occurring at a young age[4,10,11]. There are some controversial aspects to the natural history and prognosis of early onset CRC, and some clinical and pathological differences compared to CRC in elderly patients[8]. Early onset CRCs are localized mostly in the right colon, are frequently poorly differentiated, show mucin production, and can develop synchronous and metachronous tumors[12]. These differences are more marked in cases with a family history suggestive of Lynch syndrome, or with molecular characteristics like MSI[8,12-14].

There is little information about microsatellite stable (MSS) forms of CRC in young adults, not only regarding their anatomoclinical features but also regarding their molecular characteristics. For example, there is an increased proportion of MSS tumors in young patients with rectal cancer[15]. Furthermore, several studies show that some alterations in molecular markers typical of MSS early onset CRCs also occur in sporadic cases of CRC, such as modified expression of APC, β-catenin and p53[9].

The aim of our study was to characterize early onset CRC by analyzing its clinical, pathological, familial, molecular, and immunohistochemical (IHC) features. We have determined the proportion of Lynch syndrome in our series, and have compared the characteristics of the MSS and MSI groups.

Early onset of CRC in young adults used to be considered to be rare, but many recent reports suggest not only that early onset CRC reaches 8% of all CRCs, but also that it might be increasing[1,2]. Similarly, it is a common belief that early onset CRC is mainly related to hereditary forms, especially to Lynch syndrome. In our study, the presence of a familial background of CRC is confirmed in 38% of the cases, 18% fulfilling Amsterdam criteria type II for Lynch syndrome. Hereditary forms of CRC were confirmed in nine patients of the present series. One was a FAP case with an APC germline mutation, and the other eight cases were Lynch syndrome. The rate of MSI in our series is similar to that described in previous studies, ranging between 19.7% and 41%[7-9]. Twenty-nine cases showed MSS. This group showed a predominance of sporadic cases. Nevertheless, there were cases that showed a positive family history. Some of them might be associated to Familial CRC type X, namely cases with MSS tumors but fulfilling Amsterdam criteria for Lynch syndrome[21,22]. These findings, however, underline the important, but not unique role, of the known hereditary factors in this age group, prompting further searches for additional causative genes for inherited CRC.

The total sample of early age-of-onset CRCs is characterized by an important proportion of tumors that are localized in the right colon (44%), have a low-grade of differentiation (16%), produce mucin (33%), and have associated polyps (33%). Regarding pathological features, the strong trend towards low-grade differentiation and mucin production of tumors in this age group is described in the literature[7]. Other characteristics, such as synchronous and metachronous CRCs (7%) and the appearance of predominantly adenomatous polyps during the follow-up in a third of the cases, have rarely been studied previously[7,13].

Another finding is the advanced stage of the tumors at diagnosis, with more than half of the cases presenting with lymph node and/or distant metastasis in the pathological exam. This is the consequence of a delay in diagnosis, which is a characteristic of these early age-of-onset CRCs reported repeatedly in the literature[7,8,13].

The results obtained with the cyclin E antibody in the IHC study are quite remarkable. High levels of cyclin E, a G1/S phase transition controller, are found in many different tumors, including CRCs[23-25]. Cyclin E expression has only been evaluated in sporadic forms of CRC, with a variable value as a prognostic factor. Some publications suggest that lack of expression of cyclin E is associated with a faster growth of CRC, but others suggest the opposite[24,26,27]. Seventy per cent of our tumors showed lack of expression of this marker, especially the group of MSS CRCs, in which the proportion reached 86%, while the opposite occurred in the MSI group. The lack of expression of cyclin E might be associated with a poor prognosis, because expression was absent in most patients who died during follow-up (9/11), and all six stage D CRCs included in the IHC study also showed lack of expression of cyclin E. This was observed in both the MSS and the MSI groups, and in the latter group, the only case that showed lack of expression also died during follow-up. Although the sample size is small and the results must therefore be taken with caution, data related to cyclin E as a factor of poor prognosis must be validated in a larger series. In fact, it would be interesting to see if lack of expression of cyclin E corresponds with a subgroup of patients with apparently stable, near-diploid chromosomes and MSS (MACS); CRC in these patients shows an aggressive pattern and the MACS phenotype appears to be overrepresented in early-onset tumors[28,29].

Another important finding of the present study is related to the Wnt pathway. We found a high proportion of normal expression of β-catenin. This protein is an indicator of Wnt pathway dynamics[30], and the expression of β-catenin, mainly in the nucleus, is considered a good marker of the activity of the Wnt pathway[31,32]. The activation of this pathway often occurs in MSS tumors, but also in MSI tumors, independent of the age of onset[33]. Our findings, however, might indicate that the Wnt pathway is not involved in a substantial proportion of our early onset CRCs.

Early onset CRC is a heterogeneous group. To classify different subtypes with common etiology, the use of tools, such as MSI or IHC for MMR proteins, to identify an MMR system deficiency or an intact system (MSS) might be an appropriate and useful approach. All clinicopathological features analyzed in the global series tend to be more marked when the series is divided into MSI and MSS groups. MSI early onset CRCs showed characteristics similar to Lynch syndrome: earlier age of onset, predominant location in the right colon, and a high proportion of poorly differentiated tumors, in accordance with previous reports[8,13]. The same occurs with an elevated proportion of mucin-producing tumors (39%), and “signet-ring” cell tumors. MSS, on the contrary, are tumors that have an older age of onset, are mainly located in the left colon, and have a low proportion of mucinous or “signet ring” cell tumors.

From the molecular point of view, our data must be confirmed in a larger series to reach more reliable conclusions. Nevertheless, some results should be emphasized. There is a good correlation between the lack of expression of MMR proteins and MSI. This is in agreement with published data, showing a positive prospective value of the IHC of 88%-100%[34,35]. Cyclin E is expressed in most of the MSI tumors, and the opposite occurs in the MSS, as published for sporadic CRC[27]. We found a normal expression of β-catenin in most MSI and MSS tumors. Our results contradict published findings for sporadic CRC, in which a high proportion of MSS tumors show an abnormal expression of β-catenin (90%), which decreases to 65% in MSI tumors[36,37]. There are few published studies focused on early onset CRC but in these the proportion of abnormal β-catenin expression is still significant (77.2% and 42.9% for MSS and MSI, respectively)[8]. Our results, however, should be confirmed by comparing them with control groups of CRCs, to exclude the possibility that technical differences or differences in interpretation of the staining patterns, might explain these contradictory findings.

Early onset CRC has an important proportion of hereditary forms of CRC. The apparent lack of involvement of the Wnt pathway is important, as is the possible value of cyclin E as a poor prognosis factor in early onset CRC. The advanced stage at diagnosis, as well as the still not fully understood group of MSS tumors, should promote a strong effort to diagnose these tumors at an earlier stage, providing a better understanding of MSS early onset CRC.