Keywords clinical - colorectal cancer - correlation - India - molecular subtypes - pathological - profile
Introduction
The incidence of colorectal carcinoma (CRC) worldwide is 19.7 per 1,00,0000 population, with 23.6/1,00,000 in males and 16.3/1,00,000 in females.[1 ] According to GLOBOCAN 2018,[1 ] CRC ranks third in worldwide newly diagnosed cancer cases and accounts for 9.2% cancer related deaths. It is also the third most common cause of cancer-specific mortality in the Asian continent.[1 ]
CRC is a biologically, histologically, and epidemiologically heterogeneous disease. Recent studies showed that the molecular profile of CRC is also different according to the tumor site.[2 ]
[3 ] Many studies were done in the western world and few Asian countries on the different molecular types of CRCs and their correlation clinically and pathologically. Somatic MLH1 DNA methylation is associated with older age, females, proximal tumors, and more likely to be BRAF V600E mutated.[4 ] The pathological features with MSI-H CRC are mucinous histology (predominantly signet ring cell type), plenty of tumor-infiltrating lymphocytes, and poor differentiation.[5 ] BRAF-mutated tumors occur in advanced age, females, smokers, and those with right-sided tumors.[6 ] In CRC, most of the BRAF mutations are sporadic MSI tumors due to MLH1 promoter methylation.[6 ]
[7 ] Very few mismatch repair (dMMR) tumors are due to germline mutations such as in Lynch's syndrome (LS).[8 ]
[9 ] RAS-mutated CRCs were more common in males and had adenocarcinoma histology with well and moderately differentiated tumors with a microsatellite stable molecular type.[10 ]
To date, very few studies have been done on the clinical and pathological profiles of CRCs and their correlation with molecular profiles in India. The purpose of this study was to classify CRCs according to molecular subtypes and to correlate the molecular markers with the clinicopathological profile.
Aims and Objectives
To study the clinical and epidemiological profile of CRCs in a tertiary cancer care hospital in India.
To study the molecular subtypes (profile) of CRCs and their correlation with the clinicopathological profile in a tertiary cancer care hospital in India.
- To evaluate the clinical and pathological profile of CRCs.
- To determine the frequency of molecular subtypes of CRCs.
- To correlate between the molecular subtypes and their clinicopathological features.
- To determine the association between different molecular subtypes of CRCs.
Materials and Methods
A prospective noninvasive interventional study was done in patients (both inpatients and outpatients) of CRC (localized/locally advanced/metastatic) who came to our institute (Rajiv Gandhi Cancer Institute and Research Centre, Rohini, Delhi) from February 2019 to March 2020. Patients who younger than 18 years and in whom tissue was insufficient or not available for testing for at least three molecular markers out of 5 (KRAS, NRAS, BRAF, MSI, and MLH1 methylation) were excluded from this study. A sample size of 43 patients would be sufficient to detect 19.7% of incidence cases of CRC[1 ] with assumptions, 5% level of significance, and 12% minimum allowable error. Sample size calculation was done using nMaster 2.0 software (CMC Vellore). The sample size is small due to financial constraints. We had collected data of total 50 patients for this study.
Data were collected from case sheets as per the proforma attached, which included history taking, physical examination, investigations (blood tests—complete blood count, kidney function tests, and liver function tests), imaging (colonoscopy/sigmoidoscopy, contrast-enhanced computed tomography of the abdomen, whole body positron emission tomography with computed tomography), and histopathology. Mismatch repair (dMMR) protein analysis expression was tested using immunohistochemistry (IHC; BenchMark XT, Ventana Medical Systems, Inc., Tucson, AZ, United States). Germline mutation analysis in MSH2, MLH1, PMS2, and MSH6 was performed based on the results of dMMR protein analysis. KRAS, NRAS, and BRAF V600E mutation analysis was done by reverse transcription polymerase chain reaction (PCR). Methylation of the CpG islands of MLH1 was done using pyrosequencing.
Statistical Analysis
Descriptive analysis was presented in mean ± SD or median (interquartile range) according to the distribution of data. Graphs such as bar charts, pie charts, and histograms are presented. The chi-squared and Fischer exact tests were applied for data analysis using SSPS 23.0. A p -value of less than 0.05 was considered to be statistically significant.
Ethical Implication
Informed consent was taken from patients undergoing blood tests for germline testing. Scientific committee and ethics committee approval was given for this study.
Financial Implication
The study has been funded by the Research Fund from the Rajiv Gandhi Cancer Institute and Research Centre, Delhi.
Results
Clinical and Epidemiological Characteristics
The baseline characteristics of the CRC patients are presented in [Table 1 ]. The median age at presentation was 53 years and the majority of the patients were males (54%). Tumor sites were the right colon (44%), left colon (38%), and rectum (18%). Of the 50 patients with CRC, 30 and 70% were current/former smokers and nonsmokers, respectively. Eight out of 50 patients consumed greater than 200 mL of alcohol daily. The majority of them (74%) had normal a body mass index (18–25), while only two patients had obesity (≥30). None of the patients had stage I CRC, while the majority (82%) had stage III and IV CRCs. Thirty percent and 14% of patients underwent upfront resection and neoadjuvant chemotherapy with or without radiotherapy followed by resection, respectively, while the rest never underwent resection due to either metastatic disease or progressive disease following neoadjuvant treatment.
Table 1
Baseline characteristics of patients with colorectal cancer patients
No. of patients (n = 50)
Age (y), median (range)
53 (25–74)
Gender
Male
27 (54%)
Female
23 (46%)
Tumor site
Right colon
44%
Left colon
38%
Rectum
18%
Stage (clinical and pathological)
I
0 (0%)
II
9 (18%)
III
14 (28%)
IV
27 (54%)
Upfront obstruction/perforation
15/50 (30%)
Upfront liver metastases
13/27 (48%)
Pathological Characteristics
The predominant histologic subtype was classical adenocarcinoma (68%). Most of the CRCs were moderately differentiated (72%). The tumor sites were the right colon (44%), left colon (38%), and rectum (18%). Further distribution according to tumor site is depicted in [Fig. 1 ].
Fig. 1 Mismatch repair (dMMR) expression in RAS/BRAD mutant and wild-type colorectal cancers.
Half of the patients had a proliferative type of tumor morphology as seen by colonoscopy, sigmoidoscopy, or histopathological examination in the resected specimens.
LVI and PNI were not assessed in seven patients due to biopsy from the metastatic site. Nearly half of the patients (22 of 43) had LVI, while around 40% had PNI. Both LVI and PNI were seen in 23% patients. In 17 patients, peritumoral lymphocytic infiltration could not be assessed as they were small biopsies. Intraepithelial lymphocytes were absent (0/HPF), low (<3/HPF), and high (≥3/HPF) in 60, 20, and 20% of the patients, respectively. Mild to moderate intratumoral lymphocytes (1–25%) were seen in 37 of 50 patients.
Almost half of the patients (49%, 16/33) did not have any peritumoral lymphocytes (PTLs). Of the 26 resected CRC patients, 52, 15, and 23% had low, intermediate, and high tumor budding scores (TBSs).
Molecular Characteristics
There were 40% of KRAS mutation (n =20), 0% of NRAS mutation (n = 0), 4% of BRAF mutation (n = 2), 56% of wild-type CRCs (n = 28), and 22% of deficient mismatch repair (dMMR) CRCs (n = 11), as shown in [Table 2 ]. Five patients with dMMR were also KRAS mutated.
Table 2
Frequency of KRAS/NRAS/BRAF mutation, dMMR expression, and MLH1 methylation
Molecular marker
No. of patients (n = 50)
KRAS/NRAS
Wild
30 (60%)
Mutant
20 (40%)
BRAF
Wild
48 (96%)
Mutant
2 (4%)
dMMR
Proficient
39 (78%)
Deficient
11 (22%)
MLH1 promoter region (
n
= 27)
Methylation
14 (52%)
Unmethylation
13 (48%)
None of the dMMR patients had BRAF mutation. Three patients (3 out of 9) were found to be having germline deficiency in the MLH1 gene. None of the patients had any personal/past/family history of CRCs and LS-related cancers prior to their diagnosis.
Association between RAS Mutation and Clinicopathological Characteristics
In total, 30 CRCs were RAS wild-type tumors (60%). KRAS wild-type carcinomas were seen in 56% of patients older than 50 years and 63% of males, which were not statistically different from those for mutated KRAS carcinoma at 44 and 37%, respectively. RAS-mutated patients are less likely to present with upfront obstruction symptoms and advanced stages (stages III and IV) even though the numbers did not reach statistical significance. RAS-mutated tumors were associated with upfront liver metastases (69 vs. 31%; p = 0.019) and were poorly differentiated (92 vs. 50%, p = 0.020) as compared with RAS wild-type tumors, as shown in [Table 3 ].
Table 3
Association between molecular subtypes and clinicopathological characteristics in colorectal cancer patients
Clinicopathological characteristics
KRAS/NRAS
BRAF
dMMR
No. of patient (%)
Mutant, 40%
Wild, 60%
p- value
No. of patients (%)
Mutant, 4%
Wild, 96%
p -value
No. of patients (%)
Deficient, 22%
Proficient, 78%
p -value
Age
50 (100)
0.538
50 (100)
0.322
50 (100)
0.728
< 50 y
16 (32)
5 (31)
11 (69)
16 (32)
0 (0)
16 (100)
16 (32)
4 (25)
12 (75)
≥50 y
34 (68)
15 (44)
19 (56)
34 (68)
2 (6)
32 (94)
34 (68)
7 (20)
27 (80)
Gender
50(100)
0.774
50 (100)
0..493
50(100)
0.046
Male
27 (54)
10 (37)
17 (63)
27 (54)
2 (74)
25 (26)
27 (54)
9 (33)
18 (67)
Female
23 (46)
10 (43)
13 (57)
23 (46)
0 (0)
23 (100)
23 (46)
2 (9)
21 (91)
Smoking status
50 (100)
1.000
50 (100)
0.528
50 (100)
0.205
Former/current smokers
15 (30)
6 (40)
9 (60)
15 (30)
1 (67)
14 (33)
15 (30)
5 (33)
10 (67)
Never smokers
35 (70)
14 (40)
21 (60)
35 (70)
1 (3)
34 (97)
35 (70)
6 (17)
29 (83)
Alcohol
50 (100)
0.875
50 (100)
0.297
50 (100)
0.823
Yes
8 (16)
3 (38)
5 (62)
8 (16)
1 (12)
7 (88)
8 (16)
2 (25)
6 (75)
No
42 (84)
17 (40)
25 (60)
42 (84)
1 (2)
41 (98)
42 (84)
9 (21)
33 (79)
BMI
50 (100)
0.198
50 (100)
0.899
50 (100)
0.722
< 18
2 (4)
2(100)
0 (0)
2 (4)
0 (0)
2
2 (4)
0 (0)
2 (100)
18–25
37 (74)
13 (35)
24 (65)
37 (74)
2 (5)
35 (95)
37 (74)
9 (24)
28 (76)
25–30
8 (16)
3 (37)
5 (63)
8 (16)
0 (0)
8 (100)
8 (16)
1 (12)
7 (88)
> 30
3 (6)
2 (67)
1 (33)
3 (6)
0 (0)
3 (100)
3 (6)
1 (33)
2 (67)
Upfront obstruction
50 (100)
1.000
50(100)
0.345
50 (100)
0.823
Yes
15 (30)
6 (40)
9 (60)
15 (30)
0 (0)
15 (100)
15 (30)
3 (20)
12 (80)
No
35 (70)
14 (40)
21 (60)
35 (70)
2 (6)
33 (94)
35 (70)
8 (23)
27 (77)
Upfront liver metastases
26 (52)
0.019
26 (52)
26 (52)
0.000
Yes
13 (50)
9 (69)
4 (31)
10
1 (10)
9 (90)
0.605
13 (50)
0 (0)
13 (100)
No
13 (50)
2 (15)
11 (85)
16
0 (0)
16 (100)
13 (50)
0 (0)
13 (100)
Stage
50 (100)
0.454
50(100)
0.499
50 (100)
0.002
I + II
9 (18)
5 (56)
4 (44)
9 (18)
0 (0)
9 (100)
9 (18)
6 (67)
3 (33)
III + IV
41 (82)
15 (36)
26 (64)
41 (82)
2 (5)
39 (95)
41 (82)
5 (12)
36 (88)
Tumor site
50 (100)
0.687
50(100)
0.790
50 (100)
0.056
Right colon
22 (44)
10 (45)
12 (55)
22 (44)
1 (5)
21 (95)
22 (44)
8 (36)
14 (64)
Left colon
19 (38)
6 (31)
12 (69)
19 (38)
1 (5)
18 (95)
19 (38)
1 (5)
18 (95)
Rectum
9 (18)
3 (33)
6 (67)
9 (18)
0 (0)
9 (100)
9 (18)
2 (22)
7 (78)
Clinicopathological characteristics
KRAS/NRAS
BRAF
dMMR
No. of patients (%)
Mutant
Wild
p
-value
No. of patients (%)
Mutant
Wild
p-
value
No. of patients (%)
Deficient
Proficient
p
-value
T stage
50 (100)
0.904
50 (100)
0.530
50 (100)
0.010
T3
18 (36)
7 (39)
11 (61)
18 (36)
0 (0)
18 (100)
18 (36)
8 (44)
10 (56)
T4
32 (74)
13 (40)
19 (60)
32 (74)
2 (6)
30 (94)
32 (74)
3 (9)
29 (91)
N stage
50 (100)
0.454
50 (100)
0.499
50 (100)
0.002
N0
9 (18)
5 (56)
4 (44)
9 (18)
0 (0)
9 (100)
9 (18)
6 (67)
3 (33)
N1or N2
41 (82)
15 (36)
26 (64)
41 (82)
2 (5)
39 (95)
41 (82)
5 (12)
36 (88)
M stage
50 (100)
0.728
50 (100)
0.954
50 (100)
0.000
M0
24 (48)
9 (37)
15 (63)
24 (48)
1 (4)
23 (96)
24 (48)
11 (46)
13 (54)
M1
26 (52)
11 (42)
15 (58)
26 (52)
1 (4)
25 (96)
26 (52)
0 (0)
26 (100)
Tumor morphology
50 (100)
1.000
50 (100)
1.000
50 (100)
0.496
Ulcerative
25 (50)
10 (40)
15 (60)
25 (50)
1 (4)
24 (96)
25 (50)
4 (16)
21 (84)
Proliferative
25 (50)
10 (40)
15 (60)
25 (50)
1 (4)
24 (96)
25 (50)
7 (28)
18 (72)
Tumor histology
50 (100)
0.462
50 (100)
0.612
50 (100)
0.410
Classic adenocarcinoma
34 (68)
13 (38)
21 (62)
34 (68)
2 (6)
32 (94)
34 (68)
6 (18)
28 (82)
Mucinous/signet cell
15 (30)
6 (40)
9 (60)
15 (30)
0 (0)
15 (100)
15 (30)
5 (33)
10 (67)
Serrated adenocarcinoma
1 (2)
1 (100)
0 (0)
1 (2)
0 (0)
1 (100)
1 (2)
0 (0)
1 (100)
Tumor grade
50 (100)
0.020
50 (100)
0.020
50 (100)
0.019
Well/moderately differentiated
36 (72)
18 (50)
18 (50)
36 (72)
0 (0)
36 (100)
36 (72)
11 (30)
25 (70)
Poorly differentiated
24 (28)
2 (8)
12 (92)
24 (28)
2 (8)
12 (92)
24 (28)
0 (0)
14 (100)
LVI
43 (86)
0.374
43 (86)
0.323
43 (86)
0.795
Present
18 (42)
6 (33)
12 (67)
22 (42)
1 (4)
21 (96)
22 (52)
6 (33)
16 (67)
Absent
25 (58)
10 (40)
15 (60)
21 (58)
0 (0)
21 (100)
21 (48)
5 (20)
16 (80)
PNI
43 (86)
0.052
43 (86)
0.413
43 (86)
0.728
Present
17 (40)
3 (18)
14 (82)
17 (40)
0 (0)
17 (100)
17 (40)
5 (29)
12 (71)
Absent
26 (60)
13 (50)
13 (50)
26 (60))
1 (4)
25 (96)
26 (60)
6 (23)
20 (77)
LN harvest ratio
26 (52)
0.224
26 (52)
NA
26 (52)
0.114
0
12 (46)
6 (50)
6 (50)
12 (46)
0 (0)
12(100)
12 (46)
7 (58)
5 (42)
0.01–0.17
8 (30)
1 (12)
7 (88)
8 (30)
0 (0)
6 (100)
8 (30)
1 (12)
7 (88)
> 0.17
6 (24)
2 (33)
4 (67)
6 (24)
0 (0)
8 (100)
6 (24)
2 (33)
4 (67)
Tumor budding score
26 (52)
0.898
26 (52)
NA
26 (52)
0.483
Low
16 (62)
6 (37)
10 (63)
16 (62)
0 (0)
16 (100)
16 (62)
7 (44)
9 (56)
Intermediate/high
10 (38)
4 (40)
6 (60)
10 (38)
0 (0)
10 (100)
10 (38)
3 (30)
7 (70)
IEL
50 (100)
0.470
50 (100)
0.470
50 (100)
0.072
Absent/low
40 (80)
17 (42)
23 (58)
40 (80)
2 (5)
38 (95)
40 (80)
7 (17)
34 (83)
High
10 (20)
3 (30)
7 (70)
10 (20)
0 (0)
10 (100)
10 (20)
4 (40)
5 (50)
ITL
50 (100)
0.652
50 (100)
0.382
50 (100)
0.419
Absent
12 (24)
4 (33)
8 (67)
12 (24)
0 (0)
12 (100)
12 (24)
1 (8)
11 (92)
Mild/minimal
26 (52)
12 (46)
14 (54)
26 (52)
2 (8)
24 (92)
26 (52)
7 (30)
19 (70)
Moderate/high
12 (24)
4 (33)
8 (67)
12 (24)
0 (0)
12 (100)
12 (24)
3 (25)
9 (75)
PTL
33 (66)
0.560
33 (66)
NA
33 (66)
0.010
Abbreviations: BMI, Body Mass Index; BRAF, V-Raf Murine Sarcoma Viral Oncogene Homolog B, IEL, Intra-Epithelial Lymphocytes; ITL, Intra -Tumoral Lymphocytes; KRAS, Kirsten RAt sarcoma; LVI, Lympho-Vascular Invasion; M, Metastasis; NRAS, Neuroblastoma RAt Sarcoma; N, Node; PNI, Peri-Neural Invasion; PTL, Peri-Tumoral Lymphocytes; T, Tumour.
Association between BRAF Mutation Status and Clinicopathological Features
BRAF wild-type CRCs were significantly poorly differentiated than BRAF mutant-type CRCs (92 and 8%, respectively; p = 0.020).
Association between dMMR Protein Expression and Clinicopathological Features
dMMR status was done in all 50 patients. Eleven (22%) patients had dMMR. MLH1, PMS2, MSH2, and MSH6 deficiency rates were 16% (8/50), 2% (1/50), 4% (2/50), and 0% (0/50), respectively. MLH1/PMS2 and MSH2/MSH6 deficiency was seen in 18% (9/50) and 4% (2/50) of CRCs, respectively. The correlation of clinicopathological characteristics with dMMR status is presented in [Table 3 ].
Females had a higher proportion of pMMR (91 vs. 67%, p < 0.046). pMMR status was also associated with well differentiation (p < 0.022), right-sided colonic tumors (p = 0.024), and absence of PTLs. There was a definite male preponderance, with 81% of dMMR tumors detected in males. The majority of dMMR tumors were stage II cancers (67%, p < 0.001). dMMR patients had a lower propensity to invade the bowel wall (p = 0.010), nodal metastases (p = 0.006), and distant metastases. Most dMMR tumors (72%) were located on the right side of the colon. Almost half (5/11) of the dMMR tumors were mucin producing and the rest were found to have classical adenocarcinomas.
Moreover, a high number of intraepithelial lymphocytes and mild peritumoral lymphocytic infiltration was statistically associated with dMMR (40 vs. 17%, p = 0.072 and 62 vs. 38%, p = 0.010, respectively) as compared to pMMR CRCs. As seen in [Table 3 ], at the time of resection and biopsy, fewer dMMR tumors showed lymphovascular or perineural invasion and many had low lymph node harvest ratio (LNR) and TBS although they were not statistically significant.
Association between dMMR and RAS/BRAF Mutation Status
Five (25%) of the 20 CRCs with KRAS mutations were dMMR, whereas most of the CRCs (78%) in the other two subgroups (BRAF mutant and RAS/BRAF wild type) were dMMR proficient ([Table 4 ]). These associations were statistically insignificant (p = 0.714).
Table 4
Association between MLH1 promoter methylation status and RAS/BRAF mutation status
Molecular marker
MLH1 promoter
Methylation (n = 14)
Unmethylation (n = 13)
p -value
dMMR
Deficient (n = 7)
3 (43)
4 (57)
0.2500
Proficient (n = 20)
11 (55)
9 (45)
KRAS/NRAS
Wild (n = 8)
8(53)
7(47)
1.0000
Mutant (n = 6)
6(50)
6(50)
BRAF
Wild (n = 27)
14 (52)
13 (48)
1.0000
Mutant (n = 0)
0 (0)
0 (0)
Association between MLH1 Methylation and dMMR, KRAS, and BRAF
MLH1 methylation data of 27 patients were analyzed. MLH1 promoter methylation at the 5′ site was seen in 14 of 27 patients (52%). Of the seven dMMR tumors, three had MLH1 methylation and the rest were nonmethylated. The majority of dMMR proficient tumors were MLH1 methylated (55%). KRAS/BRAF mutation status and MLH1 methylation had no significant association ([Table 4 ]).
Discussion
This study demonstrates that abnormalities of the KRAS gene are an important finding in colorectal neoplasia in the Indian population. The data correlate with the KRAS mutation prevalence from different countries such as United States (44%),[10 ] Japan (33.5%),[11 ] China (40.4%),[12 ] and other studies from India.[13 ] In contrast to our results, Bisht et al[14 ] found a lower prevalence of KRAS mutation (23.5%) in Indian CRCs. Although statistically insignificant, we found the frequency of RAS mutations to be low in males and younger patients with CRC (<50 years). This is dissimilar to the findings in the Bisht et al[14 ] study, where KRAS mutations were significantly higher in older patients and females. This variable prevalence of KRAS mutation can be attributed to genetic factors, dietary factors, environmental factors, testing method, and quality of the sample.
The KRAS-mutated tumors were mostly seen in patients with classical adenocarcinoma in western studies.[10 ] On the contrary, we found it to be not statistically significant with adenocarcinoma histology. In our study, KRAS wild-type tumors were associated with well-differentiated tumors unlike the observation by Veldore et al.[13 ] This dissimilarity could be due to the small sample size. Being a rare mutation,[15 ] we could also not find any NRAS mutation in our study.
BRAF mutation frequency was found to be 4% in this study, which is higher than the reported frequencies in China (2.3%) and lower than that reported in India (9.8%). The small sample size and different sensitivities for the molecular techniques used can explain the disparity. In our study, BRAF wild-type tumors were more commonly associated with well differentiation. These findings are inconsistent with the study by Bisht et al.[14 ] As in the Li et al[16 ] study, there was no significant difference with BRAFV600E-mutated tumors according to age and sex. Furthermore, in line with prior studies and literature, none of the KRAS mutation cases had concomitant BRAF mutations, which indicates the mutually exclusive nature of these mutations. KRAS- and BRAFV600E-mutated tumors were more advanced tumors with ≥4 positive lymph nodes and higher TNM stages. However, this observation was not consistent with our results. The smaller size of the BRAFV600E mutation and KRAS mutation subgroups can explain this variation.
The 22% of CRCs with dMMR was in accordance with data from an Indian study (29%).[17 ] Reports from other Asian countries showed only 10% MSI-H CRCs.[5 ]
[18 ] This discrepancy can be due to the different molecular tests used and their sensitivities to some extent. Compared with PCR-based MSI testing, IHC is easy to perform and the turnaround time is very less. Most importantly, IHC helps in picking up and may detect few dMMR cases that may have been missed by PCR-based MSI testing.[19 ] Correlations between dMMR status and clinicopathological features were contrary with prior studies. It might be due to the different inclusion criteria, environmental factors, and the variable specificity and sensitivity of the different tests. Several studies showed a significant association of dMMR colorectal tumors with a lower TNM stage, poor differentiation, high intraepithelial lymphocytes, the presence of several intratumoral lymphocytic, and PTLs, and N0 nodal stage. We could not find any association between dMMR expression and LNR. This is in contrary to the study by Berg et al[20 ] where the authors found a significant association between MSI-H status and adequate lymph node harvest (>12).
MLH1 loss accounted for the majority dMMR CRCs (72%) and 40% of this deficiency (2 out of 5 tumors with MLH1 loss) was caused by MLH1 promoter methylation, which separates sporadic dMMR CRCs from germline mutation LS cases. This is dissimilar to Hampel et al's[21 ] study in which around 70% were sporadic tumors. Another curious finding in our study is that the family history is deceptive and misleading.[21 ] Therefore, all newly diagnosed CRC patients should be screened for LS using an IHC-based algorithm[22 ] ([Fig. 2 ]) rather than on family history. In our study, dMMR/KRAS mutation, dMMR/KRAS wild-type, pMMR/KRAS mutation, and pMMR/KRAS wild-type tumors were 10, 12, 30, and 48%, respectively, which is similar to the that reported by Ye et al.[23 ] This tumor subgrouping according to molecular subtypes is prognostic as MSS/KRAS mutant tumors had the worst survival.[24 ] Therefore, dMMR and KRAS markers will be key for the development of a molecular prognostic scoring system for CRC in the future.
Fig. 2 Flowchart of universal screening for Lynch's syndrome (LS) by immunohistochemistry in mismatch repair (dMMR) proteins in newly diagnosed cases of colorectal cancer.
This study has its limitations. There are missing histopathological and molecular data for few parameters in view of small biopsies or biopsies from metastatic sites. A relatively small sample size could have under- or overestimated the significance of the association between the molecular markers and the clinicopathological characteristics. Nevertheless, aside from the TBS, lymph node ratio, PTLs, and MLH1 methylation, the rest of the collected data were accurate to around 95% with less than 5% of missed information. Another drawback is the consideration of molecular testing in all CRC patients. However, the low incidence of CRCs in India and the short time period available for completion of this study could explain this. On the other hand, the strength of our study was prospective data collection and statistical correlation of data from one of the cohorts of CRCs (n = 50). Above all, this is the first Indian study to correlate complete RAS and BRAF analysis, dMMR status, and MLH1 methylation with CRCs' clinicopathological features and also the association between different molecular subtypes. It helped pick up additional cases for germline testing for LS.
Conclusion
In conclusion, 40, 4, and approximately one-quarter (22%) of the colorectal tumors were KRAS mutant, BRAF mutant, and dMMR, respectively. In particular, KRAS, BRAF mutation status, dMMR expression, and MLH1 methylation have unique clinical, pathological, and molecular characteristics, which must be kept in mind when assessing in clinical trials the prognosis values of different molecular markers in CRCs. Further studies including larger cohorts of CRC patients should be done to confirm these associations.
