Survival Trends of Right- and Left-Sided Colon Cancer across Four Decades: A Norwegian Population-Based Study

Abstract

Background: Patients with right-sided colon cancer (RCC) and left-sided colon cancer (LCC) differ clinically and molecularly. The main objective was to investigate stage-stratified survival and recurrence of RCC and LCC across four 10-year periods.

Methods: Patients diagnosed from 1977 to 2016 with colon adenocarcinoma were included from the Cancer Registry of Norway. Primary tumor location (PTL) was defined as RCC if proximal and LCC if distal to the splenic flexure. Multivariable regressions were used to estimate HRs for overall survival (OS), recurrence-free survival (RFS), survival after recurrence (SAR), and excess HRs (eHR) for relative survival (RS).

Results: 72,224 patients were eligible for analyses [55.1% (n = 39,769/72,224) had RCC]. In 1977 to 1986, there was no difference between LCC and RCC in OS [HR, 1.01; 95% confidence interval (CI), 0.97-1.06; P = 0.581] or RS (eHR, 0.96; 95% CI, 0.90-1.02; P = 0.179). In 2007 to 2016, LCC had significantly better OS (HR, 0.84; 95% CI, 0.80-0.87; P < 0.001) and RS (eHR, 0.76; 95% CI, 0.72-0.81; P < 0.001) compared with RCC. The gradually diverging and significantly favorable prognosis for LCC was evident for distant disease across all time periods and for regional disease from 2007 onward. There was no difference in RFS between LCC and RCC in patients less than 75 years during 2007 to 2016 (HR, 0.99; 95% CI, 0.91-1.08; P = 0.819); however, SAR was significantly better for LCC (HR, 0.61; 95% CI, 0.53-0.71; P < 0.001).

Conclusions: A gradually diverging and increasingly favorable prognosis was observed for patients with LCC with advanced disease over the past four decades.

Impact: Current PTL survival disparities stress the need for further exploring targetable molecular subgroups across and within different PTLs to further improve patient outcomes.

Figure 1.

Overview of data source and extraction, and study populations.

Figure 2.

Survival estimates for all patients stratified by four 10-year periods. Estimates of OS (solid line) and RS (dotted line) are presented for RCC (blue) versus LCC (red) in patients diagnosed during 1977–1986 (A), 1987–1996 (B), 1997–2006 (C), and 2007–2016 (D). HRs and eHRs are unadjusted, comparing LCC with RCC (reference). Numbers at risk are for OS estimates.

Figure 3.

eHRs associated with PTL according to decades for all colon cancers and different subgroups. Models are estimated separately for each time period and adjusted for age group, sex, stage, and morphology. Percentages may not total 100 due to rounding.

Figure 4.

Recurrence and survival estimates for patients diagnosed with nonmetastatic disease during 2007 to 2016. RFS is presented for RCC (blue) versus LCC (red) in patients aged 0 to 74 (A) and ≥75 (B) years. SAR is presented for RCC (blue) versus LCC (red) in patients aged 0 to 74 (C) and ≥75 (D) years. HRs are unadjusted, comparing LCC with RCC (reference).

Figure 5.

Graphical abstract summarizing main survival trends comparing LCC with RCC (reference). Top right, the overall eHRs changing over time, including yearly estimates (bullets) and a locally weighted scatterplot smoothing trend line with 95% CIs. Bottom right, estimated eHR changing over time within different subgroups, including heatmaps stratified for stage, morphology, age, and sex. NA, not available; AC, adenocarcinomas. Medical art in the top left panel was adapted from Servier Medical Art by Servier, licensed under a Creative Commons Attribution 3.0 Unported License.