A systematic review of the clinical validity of the Cologuard™ genetic test for screening colorectal cancer

Implementing a mailed stool sample screening program in clinics providing care for an underserved Hispanic population

Colorectal cancer (CRC) is a leading cause of cancer-related deaths in Hispanics in the US. Despite this, Hispanics are being screened for CRC at a much lower rate than their non-Hispanic white counterparts. Implementing mailed fecal immunochemical tests (FITs) is a cost-effective intervention for increasing CRC screening rates in vulnerable populations, such as Hispanic populations in border metroplexes. We aimed to describe the effect of introductory calls coupled with mailed in-home FIT kits on CRC screening completion in two federally qualified health centers (FQHCs) in a US-Mexico border county. This was a prospective, pragmatic, two-arm intervention study with participants allocated to receive a FIT kit with a reminder call (usual care) or usual care preceded by an introductory call. The primary outcome was the percentage of patients who returned the FIT kits. Participants who returned to the FIT were primarily unemployed (54.4%), had less than a high school education (60.2%), lived in the US for at least 20 years (74.4%), and had poor self-reported health (54.4%). In addition, we observed a statistically significant increase in the absolute rate (4.5%, P = 0.003) of FITs returned when a mailed FIT kit was preceded by an introductory call compared with no initial call. This study demonstrated that adding an introductory phone call significantly improved the screening completion rate in a mailed-out CRC screening intervention in the US-Mexico border population.

BMP3 suppresses colon tumorigenesis via ActRIIB/SMAD2-dependent and TAK1/JNK signaling pathways

Background

BMP3 gene is often found hypermethylated and hence inactivated in several types of cancers including colorectal cancer (CRC), indicating that it has a suppressor role in carcinogenesis. Though BMP3 is a reliable biomarker for screening CRC, the molecular mechanism of BMP3 in carcinogenesis remains largely unknown.

Methods

The expression level of BMP3 was examined by immunohistochemistry staining and western blot. Methylation-specific PCR (MSP) and real-time quantitative MSP were used to test the hypermethylation status of BMP3 gene. Analyses of BMP3 function in colon cancer cell proliferation, migration, invasion, and apoptosis were performed using HCT116 and KM12 cells. BMP3 was further knocked down or overexpressed in CRC cells, and the effects on cell growth of xenograft tumors in nude mice were assessed. Co-immunoprecipitation and immunofluorescence staining were used to analyze the association between BMP3 and BMPR2 or BMP3 and ActRIIB. Microarray analysis was performed to identify most differentially expressed genes and pathways regulated by BMP3. The BMP3-regulated SMAD2-dependent signaling pathway and TAK1/JNK signal axes were further investigated by quantitative PCR and western blot.

Results

BMP3 gene was hypermethylated and its expression was downregulated in both CRC tissues and cell lines. Expressing exogenous BMP3 in HCT116 inhibited cell growth, migration, and invasion and increased rate of apoptosis both in vitro and in vivo. However, shRNA-mediated attenuation of endogenous BMP3 in KM12 reversed such inhibitory and apoptotic effects. Furthermore, BMP3 could bind to ActRIIB, an activin type II receptor at the cellular membrane, thereby activating SMAD2-dependent pathway and TAK1/JNK signal axes to regulate downstream targets including caspase-7, p21, and SMAD4 that play crucial roles in cell cycle control and apoptosis.

Conclusions

Our study reveals a previously unknown mechanism of BMP3 tumor suppression in CRC and provides a rationale for future investigation of BMP3 as a potential target for the development of novel therapeutic agents to fight CRC.

Detection of KRAS G12D in colorectal cancer stool by droplet digital PCR

AIM

To assess KRAS G12D mutation detection by droplet digital PCR (ddPCR) in stool-derived DNA from colorectal cancer (CRC) patients.

METHODS

In this study, tumor tissue and stool samples were collected from 70 patients with stage I-IV CRC diagnosed by preoperative biopsy. KRAS mutational status was determined by pyrosequencing analysis of DNA obtained from formalin-fixed paraffin-embedded (FFPE) tumor tissues. The KRAS G12D mutation was then analyzed by ddPCR in FFPE tumors and stool-derived DNA from patients with this point mutation. Wild-type (WT) tumors, as determined by pyrosequencing, were included as controls; analysis of FFPE tissue and stool-derived DNA by ddPCR was performed for these patients as well.

RESULTS

Among the total 70 patients included, KRAS mutations were detected by pyrosequencing in 32 (45.71%), whereas 38 (54.29%) had WT tumors. The frequency of KRAS mutations was higher in left-sided tumors (11 located in the right colon, 15 in the left, and 6 in the rectum). The predominant point mutation was KRAS G12D (14.29%, n = 10), which was more frequent in early-stage tumors (I-IIA, n = 7). In agreement with pyrosequencing results, the KRAS G12D mutation was detected by ddPCR in FFPE tumor-derived DNA, and only a residual number of mutated copies was found in WT controls. The KRAS G12D mutation was also detected in stool-derived DNA in 80% of all fecal samples from CRC patients with this point mutation.

CONCLUSION

ddPCR is a reliable and sensitive method to analyze KRAS G12D mutation in stool-derived DNA from CRC patients, especially at early stages. This non-invasive approach is potentially applicable to other relevant biomarkers for CRC management.