The RAS gene family is among the most studied and best characterized of the known cancer-related genes. Of the three human ras isoforms, KRAS is the most frequently altered gene, with mutations occurring in 17%–25% of all cancers. In particular, approximately 30%–40% of colon cancers harbor a KRAS mutation. KRAS mutations in colon cancers have been associated with poorer survival and increased tumor aggressiveness. Additionally, KRAS mutations in colorectal cancer lead to resistance to select treatment strategies. In this review we examine the history of KRAS, its prognostic value in patients with colorectal cancer, and evidence supporting its predictive value in determining appropriate therapies for patients with colorectal cancer.

Background Mutations in KRAS and TP53 are common in colorectal carcinogenesis and are associated with resistance to therapy. Rectal cancers carrying both mutations are less likely to respond to neoadjuvant chemoradiation therapy (CRT) compared to wildtype tumors. Codon-specific KRAS mutations are associated with variable resistance to targeted therapies, but their association with rectal cancer response to CRT remains unclear. Our objective was to establish a correlation between specific KRAS mutations and rectal cancer response to CRT, and investigate if the correlation was related to a different association between KRAS and TP53 mutations. Methods One hundred forty-eight stage II–III rectal cancer patients underwent pre-operative CRT followed by surgery. DNA was extracted from pretreatment tumor biopsies and paired normal surgical tissues and KRAS and TP53 genotyping was performed. Specific KRAS mutations were then correlated with tumor response, and with concurrent TP53 mutation. Results Sixty patients had KRAS mutation; 12 in codon 13, and 48 in other locations. Eighty patients had TP53 mutation; 27 had concurrent KRAS/TP53 mutations. Tumors with any KRAS mutation were less likely to have a pCR compared to wildtype KRAS (p=0.006). Specifically, no tumors with KRAS codon 13 mutations had a pCR (p=0.03). Tumors with KRAS codon 13 mutations also had a higher incidence of concurrent TP53 mutation compared to tumors with other KRAS mutations (p=0.02). Conclusions Mutations in different KRAS codons may have different effects on rectal cancer resistance to CRT. This variable resistance may be related to a different frequency of TP53 mutations in KRAS mutant tumors.

Cancer stem cells (CSCs) have key roles in treatment resistance, tumour metastasis and relapse. Using colorectal cancer (CC) cell lines, patient-derived xenograft (PDX) tissues and patient tissues, here we report that CC CSCs, which resist chemoradiation, have higher SUMO activating enzyme (E1) and global SUMOylation levels than non-CSCs. Knockdown of SUMO E1 or SUMO conjugating enzyme (E2) inhibits CC CSC maintenance and self-renewal, while overexpression of SUMO E1 or E2 increases CC cell stemness. We found that SUMOylation regulates CSCs through Oct-1, a transcription factor for aldehyde dehydrogenases (ALDHs). ALDH activity is not only a marker for CSCs but also important in CSC biology. SUMO does not modify Oct-1 directly, but regulates the expression of TRIM21 that enhances Oct-1 ubiquitination and, consequently, reducing Oct-1 stability. In summary, our findings suggest that SUMOylation could be a target to inhibit CSCs and ultimately to reduce treatment resistance, tumour metastasis and relapse.

Background The standard treatment for locally advanced rectal cancer is pre-operative chemoradiation and total mesorectal excision. After surgery, tumors are classified according to the depth of tumor invasion, nodal involvement, and tumor regression grade. However, these staging systems do not provide information about the distribution of residual cancer cells within the bowel wall. Objective To determine the distribution of residual cancer cells in each layer of the bowel wall in rectal cancer specimens. Design Prospective Phase II study. Setting Multi-institutional. Patients 153 patients with stage II or stage III rectal cancer. Interventions Patients were treated with chemoradiation and surgery. Surgical specimen tumor tissue was analyzed and the distribution of residual cancer cells in each layer of the bowel wall was determined. Main Outcome Measures Statistical analysis was used to examine the correlation of residual cancer cells in each layer of the bowel wall with the clinical/pathological stage and tumor regression grade. Results Forty-two of 153 (27%) patients had complete response in the bowel wall (ypT0). Of the remaining 111 patients who had residual cancer cells, 5 (3%) were ypTis, 12 (8%) were ypT1, 41 (27%) were ypT2, 50 (33%) were ypT3, and 3 (2%) were ypT4. Of the 94 patients with ypT2-4 tumors, 12 (13%) had cancer cells in the mucosa and 53 (56%) had cancer cells in the submucosa; 92 (98%) had cancer cells in the muscularis propria. Pretreatment cT stage correlated with distribution of residual cancer cells. Tumor regression grade was not associated with distribution of residual cancer cells after chemoradiation. Limitations Patients received different chemotherapy regimens. Conclusions Residual cancer cells in rectal cancer specimens after chemoradiation are preferentially located close to the invasive front. This should be considered when designing strategies to diagnose complete pathologic response and when investigating the mechanisms of tumor resistance to chemoradiation.

While disparities across racial/ethnic groups are well-documented, our study is the first to identify socioeconomic disparities in survival for patients within the same group. These novel findings demonstrate the complex role of SES on race and ethnicity and identify the need to improve healthcare access even within select populations.

Recent reports have indicated that KRAS and TP53 mutations predict response to therapy in colorectal cancer. However, little is known about the relationship between these two common genetic alterations. Micro-RNAs (miRNAs), a class of noncoding RNA implicated in cellular processes, have been increasingly linked to KRAS and TP53. We hypothesized that lethal-7a (let-7a) miRNA regulates KRAS through TP53. To investigate the relationship between KRAS, TP53, and let-7a, we used HCT116 KRASmut human colorectal cancer cells with four different genotypic modifications in TP53 (TP53−/−, TP53+/−, TP53mut/+, and TP53mut/−). Using these cells we observed that K-Ras activity was higher in cells with mutant or knocked out TP53 alleles, suggesting that wild-type TP53 may suppress K-Ras activity. Let-7a was present in HCT116 KRASmut cells, though there was no correlation between let-7a level and TP53 genotype status. To explore how let-7a may regulate K-Ras in the different TP53 genotype cells we used let-7a inhibitor and demonstrated increased K-Ras activity across all TP53, thus corroborating prior reports that let-7a regulates K-Ras. To assess potential clinical implications of this regulatory network, we examined the influence of TP53 genotype and let-7a inhibition on colon cancer cell survival following chemoradiation therapy (CRT). We observed that cells with complete loss of wild-type TP53 alleles (−/− or −/mut) were resistant to CRT following treatment with 5-fluorouracil and radiation. Further increase in K-Ras activity with let-7a inhibition did not impact survival in these cells. In contrast, cells with single or double wild-type TP53 alleles were moderately responsive to CRT and exhibited resistance when let-7a was inhibited. In summary, our results show a complex regulatory system involving TP53, KRAS, and let-7a. Our results may provide clues to understand and target these interactions in colorectal cancer.

Background Pathologic complete response (pCR) to neoadjuvant chemoradiation (CRT) is an important prognostic factor in locally advanced rectal cancer. However, it is uncertain whether histopathological techniques accurately detect pCR. We tested a novel molecular approach for detecting pCR and compared it to current histopathological approaches. Study design Pre-treatment tumor biopsies and surgical specimens were collected from 96 patients with locally advanced rectal cancer treated with neoadjuvant CRT and surgery. Tumor response was categorized by tumor regression grade (TRG). Tumor DNA from pre-CRT tumor biopsies was screened for K-ras and p53 mutations. DNA from paired surgical specimens was then screened for the same mutations using highly sensitive polymerase chain reaction (PCR)-based techniques. Results Sixty-eight out of 96 (71%) pre-treatment biopsies harbored K-ras and/or p53 mutation; 36 (38%) had K-ras mutations, 52 (54%) had p53 mutations and 20 (21%) carried both mutations. Of 70 patients with TRG 1–3, 66 (94%) had a concordant K-ras and p53 mutation profile in pre- and post-treatment tissues. Of 26 patients with TRG 0 (pCR), 12 had K-ras or p53 mutations in pre-treatment biopsies. Of these, 2 (17%) patients had the same K-ras (n=1) or p53 (n=1) mutation detected in post-treatment tissue. Conclusions Sensitive molecular techniques detect K-ras and p53 mutations in post-CRT surgical specimens in some patients with a pCR. This suggests histopathological techniques may not be completely accurate, and that some patients diagnosed with a pCR to CRT may indeed have occult cancers cells in their surgical specimens with K-ras and p53 mutations serving as reliable surrogates for residual disease.

Background Microsatellite instability (MSI) is a marker of chemoresistance, but it is associated with improved survival when compared to microsatellite-stable (MSS) colon cancers. We hypothesized that MSI tumors over-express chemoresistance-associated genes and under-express DNA damage/repair genes. We used ultra high-throughput sequencing (UHTS) to assess the expression of representative genes in MSI and MSS colon cancer cell lines. Methods Solexa UHTS was used to examine gene expression in HCT116 (MSI) and HT29 (MSS) cells, and normal colonic mucosa (NCM). We compared expression of 40 genes involved in chemoresistance, DNA repair, DNA damage, and drug metabolism pathways. Results We observed gene expression differences between MSI and MSS cell lines in 8 out of 40 genes involved in mismatch repair (MMR), DNA repair, drug metabolism and chemoresistance. MMR gene expression was lower in MSI cells, which is consistent with the MSI phenotype, whereas DNA repair genes were highly expressed in these cells. Genes associated with chemoresistance and drug metabolism also had increased expression in MSI cells. No difference in expression of DNA damage genes was observed between MSI and MSS cell lines. Conclusion Using UHTS gene expression analysis, we identified differential expression of genes between MSI and MSS cell lines which may account for resistance to chemotherapy in MSI tumors. UHTS expression analysis has the potential to identify genome-wide predictors of response or resistance to chemotherapy.