Introduction:
Colorectal cancers (CRC) stand 3rd in males and 2nd in females in order of frequency of most common cancers worldwide and in developed countries, and is 4th common in males and 5th common in females in developing countries. Highest incidence rates are reported from Australia, New Zealand, Europe and North America whereas lowest rates are found in Africa and South central Asia which includes India.(1) Over the past several years, many investigators have described a change in subsite distribution of colorectal cancers towards the right side.(2-6) It is now important to establish whether the reported change in anatomical distribution is genuine in a region where the incidence rates are very low.(1) It is also important to appreciate variation in the anatomical distribution of CRC and whether this is indeed changing over a period of time as it will influence our current practices in investigating these patients. Hence the study was undertaken to know the anatomical distribution over a period of 6 years (January 2006 through 2011) at our Regional cancer center.
Materials
For our retrospective analysis, patients diagnosed with primary colorectal cancers, adenocarcinoma and mucinous (signetring) carcinomas, are included. Lymphomas, sarcomas, melanomas and carcinoid tumors were excluded. The histopathology reports, surgical reports, and case notes of each patient were reviewed from case records for age at diagnosis, gender, histology subtype, year of diagnosis, and anatomical location of the tumor. Colonic tumors located at the caecum, ascending colon, hepatic flexure, transverse colon, and splenic flexure were defined as right sided colon cancer and tumors located at the descending colon, sigmoid, rectosigmoid and rectum were defined as left sided colorectal cancer.(7) The anatomical distribution of the cancers was determined for each year during the 6 year period. If the tumor was located at the border between the two colonic subsites, it was considered a tumor of the segment wherever the majority tumor was found.
Statistical analysis: The Statistical software, namely SAS 9.2, SPSS 15.0, Stata 10.1, MedCalc 9.0.1, Systat 12.0 and R environment ver. 2.11.1 were used for the analysis of the data. Significance was assessed at 5% level of significance. Chi square test was used to know the p value and considered significant if p ≤0.05.
Results
During the study period we identified 839 patients with CRC of whom 495(59%) were males and 344(41%) were females. Right colon cancers were seen in 123 (14.7%) patients and left colon cancers in 716 (85.3%) patients. (Table 1)
| Table 1: Right and Left colon cancers during six year period with mean age. |
Side of cancer |
Number of patients |
% |
Age in years
Mean ± SD |
Age in years (Mean ± SD) |
Male |
Female |
Right colon cancer |
123 |
14.7 |
50.79± 13.86 |
50.10±14.52 |
52.23±12.43 |
Left colon cancer |
716 |
85.3 |
49.14±15.03 |
49.71±16.00 |
48.38±13.59 |
Total |
839 |
100 |
49.39±14.87 |
49.77±15.75 |
48.83±13.51 |
Age at diagnosis when compared to tumor distribution revealed no significant difference, although females were affected with right colon cancers at later age than males.
When patients age was grouped at intervals of ten, the percentage proportion of patients with right colon cancers were more than left colon cancers in the age group of 41-50, with statistically significant p value of 0.043. (Table 2) Except for this subset of age group, cancers were commoner on the left than right.(6)
| Table 2: Proportions of Right and Left colon cancers at intervals of 10 years |
Type of cancer |
Age in years |
18-20 |
21-30 |
31-40 |
41-50 |
51-60 |
61-70 |
71-80 |
>80 |
Right colon cancer(n=123) |
3(2.4%) |
7(5.6%) |
18(14.6%) |
38(30.9%) |
30(24.4%) |
19(15.4%) |
8(6.5%) |
- |
Left colon cancer(n=716) |
9(1.3%) |
90(12.6%) |
130(18.2%) |
161(22.5%) |
171(23.9%) |
112(15.6%) |
35(4.8%) |
8(1.1%) |
P value |
0.308 |
0.028* |
0.344 |
0.043* |
0.903 |
0.956 |
0.453 |
0.239 |
There was higher proportion of males with right colon cancers. In the study group with right colon cancers, males were 67.5% compared to females with 32.5% and in the other group with left colon cancers, males were 57.5% and females were 42.5%; p value was statistically significant at 0.038 for gender distribution with right colon cancers.(Table 3)
| Table 3: Gender distribution of Right and Left colon cancers. |
Gender |
Right colon cancer |
Left colon cancer |
No |
% |
No |
% |
Male |
83 |
67.5 |
412 |
57.5 |
Female |
40 |
32.5 |
304 |
42.5 |
Total |
123 |
100.0 |
716 |
100.0 |
Inference |
Males are more significantly associated with Right colon cancer with p=0.038* |
A total of 14.7% had right colon cancers and 85.3% had left colon cancers during the study period. The percentage proportion of right colon cancers increased from 12.2% in 2006 to 21.9% in 2010 with the fall in proportion to 13.1% in 2011. Likewise the percentage proportion of left colon cancers rose from 15.1% to 19.6% in 2006 and 2011 respectively. But the deviation of right colon cancers from left colon cancers was significant only in the year 2009.(Table 4)
| Table 4: Year wise sex distribution of Right and Left colon cancers. |
Side of cancer |
2006
(n=123) |
2007
(n=120) |
2008
(n=123) |
2009
(n=149) |
2010
(n=168) |
2011
(n=156) |
Right colon cancer (n=123) |
15(12.2%) |
16(13.1%) |
19(15.4%) |
30(24.4%) |
27(21.9%) |
16(13.1%) |
Left colon cancer (n=716) |
108(15.1%) |
104(14.5%) |
104(14.5%) |
119(16.6%) |
141(19.7%) |
140(19.6%) |
% deviation |
2.9% |
1.4% |
0.9% |
7.8% |
2.2% |
6.5% |
P value |
0.403 |
0.657 |
0.789 |
<0.001** |
0.563 |
0.085+ |
Again in subsite distribution of CRC, the percentage proportion of caecal cancers decreased significantly over the period, from 46.7% in 2006 to 31.3% in 2011 and percentage proportion of ascending colon and hepatic flexures cancers rose from 26.7% and 6.7% to 37.5% 18.8% respectively, both being statistically significant. But in other subsites of CRC, there was no significant change over the years or they were small numbers to deduce any conclusions. (Table 5)
| Table 5: Subsite distribution of Right and Left colon cancers through 2006 to 2011. |
Type of cancer |
2006 |
2007 |
2008 |
2009 |
2010 |
2011 |
% Change |
Right colon cancer |
Cecum |
7(46.7%) |
6(37.5%) |
8(42.1%) |
11(36.7%) |
7(25.9%) |
5(31.3%) |
-15.4 |
Ascending colon |
4(26.7%) |
5(31.3%) |
3(15.8%) |
3(10.0%) |
4(14.8%) |
6(37.5%) |
10.8 |
Hepatic flexure |
1(6.7%) |
2(12.5%) |
6(31.6%) |
6(20.0%) |
10(37%) |
3(18.8%) |
12.1 |
Transverse colon |
3(20%) |
2(12.5%) |
2(10.5%) |
6(20.0%) |
4(14.8%) |
2(12.5%) |
-7.5 |
Splenic flexure |
0(0%) |
1(6.3%) |
0(0%) |
4(13.3%) |
2(7.4%) |
0(0%) |
0 |
Total |
15(100.0%) |
16(100.0%) |
19(100.0%) |
30(100.0%) |
27(100.0%) |
16(100.0%) |
- |
Left colon cancer |
Sigmoid |
14(13%) |
16(15.4%) |
7(6.7%) |
12(10.1%) |
11(7.8%) |
13(9.3%) |
-3.7 |
Recto sigmoid |
8(7.4%) |
2(1.9%) |
6(5.8%) |
4(3.3%) |
14(9.9%) |
7(5%) |
-2.4 |
Descending colon |
1(0.9%) |
4(3.8%) |
0(0%) |
1(0.8%) |
1(0.7%) |
4(2.9%) |
2 |
Rectum |
85(78.7%) |
82(78.8%) |
91(87.5%) |
102(85.7%) |
115(81.6%) |
116(82.9%) |
4.2 |
Total |
108(100.0%) |
104(100.0%) |
104(100.0%) |
119(100.0%) |
141(100.0%) |
140(100.0%) |
- |
Discussion
The mean (SD) age at diagnosis in our study was 49.34 (+14.87) years whereas in other studies it was 70 (+11) (7), and 67.7 (+11.5).(8) The reason for having the disease at early age could be effective screening programs which are easily available in most developed countries and treating benign tumors before they become malignant. As also we should note that life expectancy at birth is much lesser in developing countries than in developed countries and also patients in the age group of >65 years are much higher in developed countries.(9)
In our study, males were affected significantly more in right colon cancers group. But elsewhere, females are reported to be affected more than the males.(10-12) Higher and better healthcare being available for men in a country like India, due to social factors, may be responsible for this variation.
Many authors have noted an increasing shift from left sided colon cancers to right sided colon cancers (2-5), but not all reports are in agreement.(13) We noticed the increasing trends for both right colon cancers and left colon cancers over the study period, probably because of rising population trends. But significant deviation (shift) towards the right colon cancers occurred only in year 2009 (p <0.001). As the difference in percentage deviation is statistically not significant, the present study concludes that there is no actual migration of colon cancers towards right side.
Whereas the present study had a total 14.7% of right colon cancers during the 6 year period, other studies had 28% (10) and 31% (7) of right colon cancers. The reasoning for lower proportion in our study requires to be established by further more studies.
Conclusions:
Although the reports claim there is a true shift (migration) of cancer towards right colon cancers, our institute based analysis shows no such shift. Our study also revealed significantly higher proportion of males being affected with right colon cancers group whereas other studies have shown higher incidence among females. As the mean age at presentation was earlier than in the developed countries, it is essential to have effective screening programs. There is need for further studies based on population.
Acknowledgements: Thanks to Dr.K.P.Suresh, Ph.D (Biostatistics) Scientist(SS), Project Directorate on Animal Disease Monitoring and Surveillance (PDADMAS), Hebbal, Bangalore 560024 for his guidance in statistical analysis.
Conflict of Interest: None.
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