Microsatellite instability and early onset colorectal cancer in an emerging economy: A study in an Indonesian tertiary hospital.

Introduction

Colorectal cancer (CRC) is consistently among the top leading case of cancer in terms of incidence worldwide, ranking 4^th in male and 2^nd in female.¹ Rising incidence of CRC possess significant burden of disease with projected increase of cases up to 3,154,674 cases by 2040.² Although previously considered rare in Asian countries, it has been observed that there are an increased incidence of CRC cases in Asian populations, possibly due to exposure to risk factors such as western diet, smoking, lack of physical activity, and aging population.³ In Indonesia, number of CRC case has reached 12.4 cases per 100,000 individuals.¹

Another alarming observation is rising number of early-onset CRC (EOCRC). One study based on CRC registry in USA reported annual increase of age-adjusted incidence rate of EOCRC by 1.3% in 1996 to 2016.³ Similar findings are also reported in Asia-Pacific region with increasing mortality rate especially in Southeast Asia.⁴ In Indonesia, previous study found annual percentage change of EOCRC reaching 1.98% from 2009 to 2019.⁵ Although the exact pathomechanism leading to EOCRC is not well understood, complex interplay between genetic predisposition and environmental factors is believed to play a big role.⁶

Many studies have explored the incidence of EOCRC and several reported its association with Microsatellite Instability (MSI).^7,8 MSI, which is responsible for 20% of CRC cases, happens when there is a mutation in mismatch repair (MMR) genes.⁹ MSI has gained attention due to its implication in diagnosis and treatment of CRC. Guidelines recommend MSI testing in newly-diagnosed CRC to determine possibility of the case being hereditary and to determine prognosis.^10,11 In addition, MSI testing also provides options for CRC treatment as Microsatellite Instability High (MSI-H) patients are candidate for treatment using Programmed Death-Ligand 1 (PDL-1) inhibitor therapy.¹² MSI-H CRC tumors have distinct properties compared to Microsatellite Stable (MSS) counterpart, such as MSI-H mostly associated with right-sided tumor,¹³ mostly found in earlier stages,¹⁴ and have better prognosis.¹⁵ There are many ways to conduct MSI testing including immunochemistry, single-molecule molecular inversion probes, next generation sequencing, and fluorescent multiplex polymerase chain reaction and capillary electrophoresis.¹²

The cause of EOCRC rise and possible role of MSI in its patomechanism in Indonesia setting is still not well understood. In addition, there are not any recommendation for CRC MSI testing in Indonesia due to limited data of its significance. To author’s knowledge, there are currently only one study that provides insight of CRC MSI status in Indonesia but the data is limited to a single center.¹⁶ As Indonesia is a multiethnic and diverse country, more data of CRC MSI status from another center is needed to justify MSI testing in CRC diagnosis. This study aims to explore CRC MSI status in Indonesian patients to better understand role of MSI in EOCRC rise and role of MSI in CRC screening.

Methods

Results

Among 100 subjects with Colorectal Cancer (CRC) included in this study, 12 of them (12.4%) had Microsatellite Instability High (MSI-H) while the rest was found to be Microsatellite Stable (MSS). Among the samples, 34 (34%) of our CRC cases were early onset. Our study found a significant difference for location of tumor between MSI-H and MSS in which larger percentage of MSI-H tumor was right-sided (33.3%) than left-sided (9.7%). On the other hand, no significant difference was found in terms of gender and performance status between MSI-H and MSS. In our study, a decrease of MSI-H prevalence was found as the CRC stage increases (33.3%, 41.7% and 25.0% for stage II, III, and IV respectively) although the difference did not reach statistical significance.

Discussion

Early onset colorectal cancer has attracted attention of researchers and clinicians alike. Previous study found that as much as 41.4% of colorectal cancer cases in Indonesia are early onset.¹⁷ This result is in line with our study, in which we found that 34% of our subjects are categorized as early onset. This phenomenon begs the question on what causes early colorectal cancer cases in Indonesia and whether there are any therapies that can be done specifically to early CRC.

As the colon is a natural habitat for bacterial communities and contains around 100 trillion organisms, dysfunction of the microbiome may foster chronic inflammation and produce metabolites that are carcinogenic in nature. The high prevalence of early onset colorectal cancer may be attributed to the high prevalence of infectious diseases that occur in Indonesia.¹⁸

According to Dermawan et al. Typhoid fever is the 5th most prevalent disease in Indonesia in during 2020. There are emerging evidence that discuss the pathogenesis of colorectal cancer due to salmonella infection.¹⁹ Tumorigenesis is a multistep process that includes sustaining proliferative signaling, evasion of growth suppressors, resistance to apoptosis, replicative immortality, induction of angiogenesis and activation of invasion and metastasis.¹⁸

Microbes have been found to contribute to the development of tumors and may alter the microenvironment to be favorable for tumor growth. Salmonella infections may have varying outcomes which ranges from mild acute gastroenteritis to severe infections that are potentially fatal. Salmonella infections may also progress from acute to a chronic carrier state. Prolonged inflammation causes normal cells to develop dysplasia that could progress to cancer. A paper published by Jun Sun in 2022 found a significant increase in colorectal tumor incidence in mice inoculated with Salmonella in comparison to mice without bacterial infection.¹⁸

MSI has gained popularity as a marker to be evaluated after diagnosis of CRC.²⁰ MSI-H tumors are known to have better prognosis at early stage²¹ and are target of PDL-1 inhibitor therapy.²² We have found several differences between our study and previous study that had been conducted in Indonesia. In our study, we found 12.4% of our subjects were MSI-H, whereas previous study found 19% of their subjects were MSI-H. In addition, in our study we found 21.2% of early onset subjects were MSI-H, whereas previous study reported as much as 30% of their early onset group were MSI-H.¹⁶ One of possible causes of this differences is the diversity of genetic profiles of the subjects.²² Cipto Mangunkusumo National General Hospital, where this study was conducted, is the national referral hospital of Indonesia and therefore its patients come from different regions with diverse ethnicity.

In this study, no significant differences were found in CRC stage, tumor location, gender, BMI, and MSI status between early and late onset colorectal cancer subjects. Previous studies have found MSI-H are mostly found in early onset colorectal cancer.^8,23 Contrary to previous findings, we found that MSS dominate early colorectal cancer when compared to MSI. Indeed, our subjects were mostly at late stages which could explain the dominance of MSS due to shifting of nature of colorectal cancer from MSI to sporadic. In addition, there is a possibility of unique pathway of carcinogenesis, as stated in previous study by Susanti et al called “accelerated carcinogenesis” which may be investigated further in future studies.¹⁶

The location of CRC is significant in relation to the MSI status, in which the right side has a larger percentage than the left side (OR 0,21), CI 0,059-0,780). The trend in our study has found CRC in MSI-H patients are predominantly right sided (33.3%) than left-sided (9.7%). This is in line with a review by Gopal et al. in 2023 which described that CRC in MSI-H tends to be right-sided.¹³ This may be attributed to the distinct gene expression profiles of the right colon, including a higher rate of immune cell infiltration and different patterns of mucin production, which might influence tumor development and immune surveillance. The right colon’s gene expression profile often includes higher levels of genes associated with mismatch repair deficiencies, such as MLH1 and MSH2, which are crucial for maintaining genomic stability. When these genes are mutated or downregulated, it contributes to MSI, leading to a higher frequency of MSI CRCs in the right colon.²⁴

Patients with MSI-H are also known to benefit from PDL-1 inhibitor therapy. MSI-H is associated with accumulation of neoantigens which causes accumulation of PDL-1, resulting in greater expression compared to its MSS counterpart.²¹ In our early onset subjects, most PDL-1 test showed negative result. This phenomenon may be due to our population that is dominated by late-stage CRC and therefore most likely dominated by sporadic CRC. However, when comparing between our MSI-H and MSS group, we found PDL-1 positive were mostly found in MSI group. This warrant clinicians to conduct PDL-1 examination in MSI-H patients that may benefit from PDL-1 inhibitor. This approach should be done for both early and late onset colorectal cancer. Despite our study having several limitations including limited number of subjects, markers examined, and lack of lymphocyte workups, our study has confirmed result of previous study which is the high number of early colorectal cancer cases with MSI-H in Indonesia. As most of the cases are MSS, further study should be considered to explore its multiomic aspects in order to find possible novel carcinogenesis pathways. Other key point that should be noted is that most of CRC cases found at our center were late stages due to delay in diagnosis, highlighting importance of early detection in Indonesia. In addition, lower age limit of detection should be considered for CRC screening in Indonesia due to high number of early onset CRC cases, as reflected on the result of this study. Because Indonesia still has limited data on CRC profile, we figure genetic workups as screening approach of CRC is still not viable to be conducted in Indonesia.

Data for microsatellite instability

Harvard Dataverse: Data for Microsatellite Instability, https://doi.org/10.7910/DVN/ONXE2E.²⁵

Data are available under the terms of the Creative Commons Zero “No rights reserved” data waiver (CC0 1.0 Public domain dedication).