The Thai Cancer, 2021, 31.64.010
Abstract
Backgrond: The guideline recommends the use of anti-epidermal growth factor receptor
monoclonal antibodies (anti-EGFR Ab) as the first-line treatment only for patients with left-sided
RAS wild type (RASwt) metastatic colorectal cancer (mCRC). However, there are no
recommendations on tumor sidedness in subsequent lines. This study aims to evaluate the effect
of primary tumor location on second- or later-line treatment outcomes in patients with KRASwt
mCRC.
Method: Medical records of patients diagnosed with mCRC at Siriraj Hospital between 2008 and
2019 were retrospectively reviewed. Patients with KRASwt who received anti-EGFR Ab in the
second- or later-line treatment were included. The impact of tumor-sidedness on the progression-
free survival (PFS) was determined using the Kaplan–Meier method and compared using the log-
rank test.
Results: Of 671 patients who had data on KRAS analysis, 396 (59%) had KRASwt. Of these, 210
patients received anti-EGFR Ab in the second- or later-line treatment. Twenty-nine percent of
patients (60 out of 210) had extended RAS analysis. Thirty patients (14%) had right-sided tumors,
while 180 (86%) had left-sided tumors. Sixty-nine percent of patients (146 of 210) were treated with
anti-EGFR Ab in the third line, while 19% and 12% were treated in the second and fourth lines,
respectively. Single-agent irinotecan was the most commonly used chemotherapy backbone
(92%). Patients with right-sided tumors had non-significantly inferior PFS compared with patients
with left-sided tumors (median PFS was 4.7 months, 95% CI 0.8–8.7 vs. 6 months, 95% CI 4.6–
7.3; p = 0.55). Subgroup analysis on the impact of primary tumor location showed no difference in
PFS when stratified by treatment lines.
Conclusion: This study demonstrated that tumor sidedness has no impact on treatment
outcomes in patients treated with anti-EGFR Ab in second- or later-line treatment. Therefore, there
is not enough evidence to use tumor sidedness for treatment selection in these settings. A
multicenter retrospective cohort study is ongoing.