Background
Esophageal cancer (EC) is the most common type of cancer worldwide but is least studied with poor survival and highly aggressive nature. Various risk factors have been associated with EC which include lifestyle, dietary habits, low socio-economic status, poor oral hygiene, and genetics [
1]. According to a survey by GLOBOCAN in 2018 about 572,034 of new cases and 508,585 deaths were reported worldwide about EC. About 70% of cases have been observed in men, and there is a 2–3 fold difference in incidence and mortality rates between the sexes worldwide [
2]. In India, the Northeastern states like Assam, Meghalaya, Mizoram, and Nagaland tops the chart about EC, for both men and women. Kashmir valley is another state with the highest incidence of EC [
3]. Genetics is one of the major risk factors associated with EC which includes loss and gain of chromosomes, gene amplification, and microsatellite instability [
4]. 90% of esophageal cancers are ESCC (esophageal squamous cell carcinoma) and about 5% are EAC (esophageal adenocarcinoma) throughout the world. The remaining 5% include rare malignancies [
4]. We attempted to investigate the role of cancer-related genetic variants in ESCC within the population of J&K. J&K is an ignored state owing to its peculiar geographical background and political circumstances. Although the incidence rate of EC is very high, yet the data related to the genetics of ESCC in the studied population is meager. Replication studies are important to enhance the credibility of a study. Genes that have been explored about ESCC within the population of J&K are summarized in the (Supplementary Table
1).
Results
This is a case-control study that includes 166 ESCC cases and 592 healthy controls belonging to the Northern region of India. The mean age and standard deviation (SD) for cases were 60.4 ± 12.6 and for controls it was 58.4 ± 18.4. A total of 86 males and 80 females (cases) and 192 males and 400 females (controls) were recruited in the study. The BMI which is one of the main risk factors for malignancies was also recorded. The BMI of patients was 21.1 ± 5 and in the case of controls it was 27.6 ± 5.1. In about 68 cases there was metastasis while in 98 cases were non-metastatic. While recording family history, it was observed that about 22 cases had a family history of ESCC, 46 cases did not have a family history and 98 cases were not aware of the history of ESCC in their families. In the present study, two SNPs were showing an increased risk of ESCC within the population. These SNPs are rs12190287 of
TCF21 and rs10046 of
CYP19A1. In our study, the genetic variant rs12190287 has been evaluated concerning ESCC and it was observed that the variant under study was associated with the higher risk of ESCC within the population of Jammu and Kashmir with OR 1.412 (1.09–1.8, at 95% CI,
p = 0.008). The genetic variant in
CYP19A1 (Cytochrome P450 family 19 sub-familyA1) rs10046 (C > T) has been associated with a higher risk of ESCC with OR 1.584 (1.21–2.072, at 95% CI,
p = 0.007) as shown in Table
1.
Table 1Association analyses of the variants with Esophageal Cancer
1 | rs12190287 | TCF21 | 0.008 | 1.4 (1.09–1.8) | 0.126 | 1.3 (1.07–1.8) | 0.002 |
2 | rs10046 | CYP19A1 | 0.0007 | 1.5 (1.21–2.0) | 0.195 | 1.8 (1.1–3.2) | 0.02 |
3 | rs2735940 | TERT | 0.457 | 1.1 (0.84–1.45) | 0.499 | 1.1 (0.4–2.4) | 0.849 |
4 | rs751402 | ERCC5 | 0.597 | 0.9 (0.68–1.24) | 0.847 | 1.2 (0.7–2.0) | 0.535 |
5 | rs2699887 | PIK3CA | 0.063 | 0.7 (0.49–1.02) | 0.117 | 1.8 (1.0–3.2) | 0.03 |
6 | rs3792152 | REV1 | 0.094 | 1.2 (0.96–1.60) | 0.412 | 1.5 (0.8–2.8) | 0.170 |
7 | rs10069690 | TERT | 0.994 | 0.9 (0.72–1.3) | 0.709 | 1.0 (0.5–1.7) | 0.952 |
8 | rs2981582 | FGFR2 | 0.594 | 1.1 (0.82–1.39) | 0.067 | 1.3 (0.7–2.1) | 0.314 |
9 | rs1695 | GSTP1 | 0.723 | 1.1 (0.77–1.43) | 0.908 | 1.3 (0.7–2.3) | 0.269 |
10 | rs251796 | TERF2 | 0.299 | 0.8 (0.65–1.13) | 0.864 | 0.7 (0.4–1.2) | 0.270 |
11 | rs2229080 | DCC | 0.199 | 1.1 (0.91–1.54) | 0.113 | 0.6 (0.2–1.2) | 0.173 |
12 | rs1801018 | BCL2 | 0.999 | 1.0 (0.77–1.29) | 0.125 | 0.9 (0.5–1.6) | 0.773 |
In the present study, all the genetic variants were tested individually in a standard way to find its association with the disease. Both significant and non-significant SNPs are equally important for SNP analysis in the case-control study design. The SNP is said to be significantly associated or not associated with the risk of disease based on the
p-value. If the p-value is less than or equal to a specific threshold (0.05), the SNP is said to be significantly associated with the higher risk of the disease provided OR (odd’s ratio) is above 1 at 95% CI (confidence interval) and if the p-value is greater than 0.05 then the variant is considered to be not associated [
8]. The details of both significant and non-significant SNPs have been given in Table
1. All the SNPs summarized in the table below were following HWE. In any genetic association study, HWE is an essential tool to find genotyping errors [
9].
Discussion
Esophageal cancer is a very belligerent type of carcinoma with a very low survival rate. It’s because of its truculent nature, it is least studied worldwide. There are numerous risk factors associated with esophageal carcinoma which include genetic factors and environmental factors [
10]. In Asia, ESCC is the most prevalent type of cancer while as in Caucasians there is a higher incidence of EAC. It is because of the different heritage backgrounds that these two populations show different susceptibilities towards esophageal carcinoma [
11]. Epidemiological studies have shown that esophageal carcinoma is highly prevalent in the state of Assam located in the eastern region of India [
12]. Jammu and Kashmir are one of the high incidence areas of
“Central Asian esophageal cancer belt”. Central Asian esophageal cancer belt includes northern China, republics of Kazakhstan, Uzbekistan, and Turkmenistan. Kashmir Valley also falls under this high incidence region at the southernmost end [
4]. The State of Jammu and Kashmir is geographically divided into three distinct regions Jammu, Kashmir, and Ladakh. They are culturally and ethnically distinct. These regions have historically/geographically married within their communities thus preserving the genetic pool. Though various esophageal carcinoma studies from the Kashmir region have explored demography and genetics but it remains uninvestigated from the Jammu region. There is a major difference between the dietary habits of people from Jammu as compared to people from the Kashmir or the Ladakh region [
13]. A detailed questionnaire was designed for the patients in the present study which consisted of information like family history, age, gender, BMI, etc.
In the present study, genetic elucidation among cases and controls was explored. Genetics is an important risk factor associated with esophageal carcinoma. In the SNP analysis we have replicated the newly identified variants (rs12190287 of TCF21, rs10046 of CYP19A1, rs2735940 of TERT, rs751402 of ERCC5, rs2699887 of SLC14A2, rs3792152 of REV1, rs10069690 of TERT, rs2981582 of FGFR2, rs1695 of GSTP1, rs251796 of TERF2, rs2229080 of DCC, rs1801010 of BCL2. Two SNPs that were showing an increased risk of ESCC within the population of our study are rs12190287 of TCF21 and rs10046 of CYP19A1.
TCF21 (Transcription factor 21) helps in epithelial differentiation and thus plays a specific role in the differentiation of one or more subsets of epicardial cell types {Copyright© 1996–2018#97}. It is a candidate tumor suppressor located at chromosome 6 and it has been associated with lung, head, and neck cancers. It was found that
TCF21 in gastric carcinoma cells was highly methylated than in the normal adjacent cells. rs12190287 (C > G) of
TCF21 has been studied with Osteosarcoma risk in the Chinese population and was showing a higher risk of Osteosarcoma in the studied population [
14].
CYP19A1 (Cytochrome P450 family 19 sub-familyA1) gene plays an important role in the biosynthesis of estrogen and it has been associated with the progression of breast cancer in the Chinese population [
15]. Several association studies have been done with
CYP19A1 and it was observed that there are enormous inter-population differences. The genetic variant rs10046 (C > T) has been significantly associated with Iranian women, Inuit women, and Xinjiang Uygur women [
16].
Both the genetic variants rs12190287 of
TCF21 and rs10046 of
CYP19A1 have been studied in multiple cancers which include breast, lung, neck, and gastric cancer. Our study associated the above genetic variants with ESCC within the population of Jammu and Kashmir. The functional aspects of the variants understudy are yet to be evaluated. A recent study has observed that genetic variants that have been previously associated with one cancer are associated with other cancers too. Cross cancer analysis has been done for the identification of variants to estimate the genetic correlation between them by using the data from GWAS. Substantial evidence has been found which has identified pleiotropy among loci with strong association. A new high throughput study must be used to evaluate the functional implication of the variants [
17].
The genes (Table
1) that were not associated with the ESCC in the studied population include
TERT(Telomerase Reverse Transcriptase) which is highly active in cancer cells but shows low or inactivity in normal somatic cells. rs2735940 was significantly associated with a higher risk of ESCC in the Chinese population. This genetic variant has previously been associated with breast cancer in the European population [
18,
19]. rs751402 of
ERCC5 (Excision Repair Cross Complementing Group 5) plays an important role in DNA damage and repair and its deficiency can lead to genomic instability and carcinogenesis [
20]. There are two genetic variants rs751402 (C > T) and rs2298881 (A/C/T) rs751402 that have been associated with ESCC in the Chinese population and rs2298881 has been associated with other cancers like lung, gastric and laryngeal cancers across the population [
21‐
23]. rs2699887 of
PIK3CA(Phosphatidylinositol-4-5-Biphosphate 3-Kinase Catalytic Sub- Unit Alpha) has been associated with ESCC in the USA (Texan population). rs3792152 of
REV1(REV1, DNA Directed Polymerase) recruits DNA polymerases involved in translesion synthesis (TLS) of damaged DNA. Genetic variant rs3792152 of
REV1 is associated with breast cancer risk in Thai women [
24] and
rs2981582 ofFGFR2(Fibroblast Growth Factor Receptor 2) plays a vital role in the cell proliferation, migration, and apoptosis [
25]. Genetic variant rs2981582 of
FGFR2 has been associated with breast cancer in different women population (Dutch, Arabic, and West Siberia) [
26‐
28]. rs1695 of
GSTP1(Glutathione S-transferase Pi 1) belongs to a family of enzymes that play an important role in detoxification by catalyzing the conjugation of many hydrophobic and electrophilic compounds. The genetic variant rs1695 of GSTP1 has shown an increased risk of ESCC and EAC in the population of Kashmir Valley [
29]. In the present study, though the genetic variant rs1695 of GSTP1 has shown no significant association with ESCC. Similar results were obtained after stratification by race (Caucasian/Asian). Our results were in agreement with the above-mentioned meta-analysis of 52 studies [
30]. rs2229080 of
DCC(Deleted in Colorectal Carcinoma Netrin1 Receptor) has been studied in the Chinese population concerning breast cancer and it was found that this variant has been associated with reduced breast cancer risk [
31]. The genetic variant rs2229080 (C > G) has been studied in ESCC and gastric cancer patients in Kashmir Valley also and it has been observed that rs2229080 of
DCC has shown no association with the risk of ESCC. Various studies have shown the role of
DCC in colorectal carcinoma, gastric, breast, esophageal and prostate cancer [
32]. rs1801018 of
BCL2(B-cell lymphoma 2) contributes to programmed cell death and apoptosis and has been studied in ESCC in the Chinese population but there was no significant association observed between the variant and the risk of the disease [
33]. All of the above-mentioned SNPs have shown non-significant association with ESCC within the population of J&K in the present study. Although, these variants need to be investigated in the large cohort of population for a conclusive statement.
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