Table 2. Multivariable Analyses of Survival in Patients with Stage IV Colorectal Cancer Who Had or Had Not Undergone Primary Tumor Resection.
| PTR rate (%) | HR (95% CI) in PTR patients compared with non-PTR patients |
||||||
|---|---|---|---|---|---|---|---|
| Standard Cox regression analysis |
Instrumental variable analysisa |
||||||
| Overall survival | Cancer-specific survival | Other-cause survival | Overall survival | Cancer-specific survival | Other-cause survival | ||
| Primary analysis | |||||||
| All patients | 27 931/44 514 (62.7) | 0.45 (0.44–0.46) | 0.44 (0.43–0.45) | 0.57 (0.52–0.62) | 0.50 (0.49–0.52) | 0.50 (0.49–0.51) | 0.54 (0.49–0.59) |
| Subgroup analyses | |||||||
| Patients aged ≤ 65 y | 13 902/22 058 (63.0) | 0.44 (0.43–0.45) | 0.44 (0.42–0.45) | 0.52 (0.45–0.61) | 0.51 (0.49–0.53) | 0.50 (0.48–0.52) | 0.64 (0.55–0.75) |
| Patients aged > 65 y | 14 029/22 456 (62.5) | 0.46 (0.44–0.47) | 0.45 (0.43–0.46) | 0.57 (0.51–0.64) | 0.49 (0.47–0.51) | 0.49 (0.48–0.51) | 0.47 (0.42–0.53) |
| Sensitivity analyses | |||||||
| Metro counties | 10 587/14 744 (71.8) | 0.45 (0.44–0.46) | 0.44 (0.43–0.45) | 0.56 (0.50–0.61) | 0.50 (0.49–0.51) | 0.49 (0.48–0.51) | 0.54 (0.49–0.60) |
| Nonmetro counties | 17 344/29 770 (58.3) | 0.47 (0.44–0.50) | 0.46 (0.43–0.49) | 0.61 (0.47–0.80) | 0.52 (0.49–0.56) | 0.54 (0.50–0.57) | 0.48 (0.36–0.64) |
| Diagnosis years 1988–1999 | 23 758/38 013 (62.5) | 0.44 (0.42–0.45) | 0.43 (0.41–0.45) | 0.50 (0.43–0.59) | 0.46 (0.44–0.48) | 0.46 (0.44–0.48) | 0.42 (0.36–0.49) |
| Diagnosis years 2000–2010 | 4 173/6 501 (64.2) | 0.47 (0.46–0.49) | 0.46 (0.45–0.48) | 0.61 (0.54–0.68) | 0.55 (0.53–0.56) | 0.55 (0.53–0.56) | 0.57 (0.51–0.64) |
Abbreviations: HR, hazard ratio; PTR, primary tumor resection.
aHRs were derived from a two-stage residual inclusion model using the Weibull distribution. Multivariable survival analyses were adjusted for year of diagnosis, age, sex, race/ethnicity, marital status, tumor grade, and tumor location when applicable.