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Cancer Chemother Pharmacol (2014) 73:409–416DOI 10.1007/s00280-013-2367-7

ORIGINAL ARTICLE

CA19‑9 level as a prognostic and predictive factor of bevacizumab efficacy in metastatic colorectal cancer patients undergoing oxaliplatin‑based chemotherapy

Yukiya Narita · Hiroya Taniguchi · Azusa Komori · Sohei Nitta · Kazuhisa Yamaguchi · Chihiro Kondo · Motoo Nomura · Shigenori Kadowaki · Daisuke Takahari · Takashi Ura · Masashi Andoh · Kei Muro

Received: 31 July 2013 / Accepted: 2 December 2013 / Published online: 10 December 2013 © Springer-Verlag Berlin Heidelberg 2013

Conclusion Our results suggest that baseline CA19-9 level is an independent prognostic factor in mCRC patients, and it correlated with the KRAS/BRAF mutation sta-tus. Bevacizumab exhibits clinical activity only for high CA19-9 levels in mCRC.

Keywords Bevacizumab · Carbohydrate antigen 19-9 · Colorectal cancer · Predictive factor · Prognostic factor

Background

Colorectal cancer is the fourth leading cause of cancer-related deaths in both sexes, causing an estimated 608,000 deaths worldwide in 2008 [2]. The 5-year overall survival rate of metastatic colorectal cancer (mCRC) patients remains low [2, 10]. Several prognostic factors for mCRC patients were found in previous studies. Köhne et al. [11] identified three risk groups of mCRC patients receiving 5-fluoroura-cil (5-FU)-based chemotherapy and developed a prognostic model centered on four baseline parameters: performance status, white blood cell count (WBC), alkaline phosphatase (ALP) levels, and number of metastatic sites. The addition of bevacizumab, an antibody drug that binds vascular endothe-lial growth factor (VEGF), to chemotherapy regimens improved mCRC patient outcomes in first-line treatments [5, 17]. Some studies suggest that the efficacy of bevacizumab does not depend on KRAS or BRAF mutation status [9, 16], although VEGF-D levels in tumor tissue may predict the effectiveness of bevacizumab treatment in combination with chemotherapy [23]. However, the value of VEGF-targeted therapy for patients with mCRC has not been established.

Carbohydrate antigen 19-9 (CA19-9) [21] was first iso-lated from a colorectal cancer cell line, and it is a standard tumor marker for pancreatic cancer [8]. Although CA19-9

Abstract Purpose The prognostic and predictive values of carbo-hydrate antigen 19-9 (CA19-9) levels in metastatic colorec-tal cancer (mCRC) remain unclear. We reviewed all mCRC patients at a single institution to evaluate the relationship between CA19-9 levels and survival.Methods Two hundred and fifty-two patients underwent first-line chemotherapy using oxaliplatin-based regimens between April 2005 and December 2009. The relationship between baseline CA19-9 levels and survival was analyzed. Moreover, we evaluated the relationship between baseline CA19-9 levels and clinicopathological factors.Results One hundred and fifty patients had elevated base-line CA19-9 levels (elevated group), and 79 patients had normal baseline CA19-9 (normal group) levels. Both KRAS and BRAF mutation rates were higher in the elevated group than in the normal group. Elevated CA19-9 level was a poor prognostic factor compared with normal CA19-9 lev-els (P = 0.0021). In the elevated group, the median survival time with bevacizumab was significantly longer with beva-cizumab than without it (median OS, 27.8 vs. 15.3 months, P = 0.0019). However, the median survival time was not different with or without bevacizumab in the normal group (median OS, 36.5 vs. 38.0 months, P = 0.9515).

Electronic supplementary material The online version of this article (doi:10.1007/s00280-013-2367-7) contains supplementary material, which is available to authorized users.

Y. Narita (*) · H. Taniguchi · A. Komori · S. Nitta · K. Yamaguchi · C. Kondo · M. Nomura · S. Kadowaki · D. Takahari · T. Ura · M. Andoh · K. Muro Department of Clinical Oncology, Aichi Cancer Center Hospital, 1-1 Kanokoden, Chikusa-ku, Nagoya, Aichi 464-8681, Japane-mail: yukiya.narita@aichi-cc.jp

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is overexpressed in 39 % mCRC patients [7], its levels alone are insufficient for monitoring colorectal cancer treat-ment according to American Society of Clinical Oncology guidelines [13]. CA19-9 acts as an adhesion factor for cells lining the blood vessels [21]. Furthermore, the association between CA19-9 levels and the efficacy of bevacizumab treatment remains unclear.

The aim of this study was to determine the usefulness of pretreatment CA19-9 levels for predicting the survival and bevacizumab treatment efficacy in mCRC patients. We analyzed (1) the prognostic impact of baseline CA19-9 lev-els for mCRC patients receiving oxaliplatin-based first-line chemotherapy and (2) their ability to predict bevacizumab treatment efficacy.

Patients and methods

Patients

This study was a retrospective cohort study of mCRC patients who received oxaliplatin-based regimens (includ-ing FOLFOX-4, modified FOLFOX-6, and CapeOX) as first-line chemotherapy at Aichi Cancer Center Hospital. Patients were aged >20 years, had histologically proven inoperable colorectal cancer, and had serum CA19-9 levels available within 4 weeks of starting chemotherapy. Patients were excluded if they had double cancer or had previously undergone chemotherapy for advanced disease.

CA19-9 level measurement

CA19-9 levels were measured at a certified laboratory in our institution using LUMIPULSE f® (Fujirebio, Inc.,) [15]. Reference range for normal CA19-9 levels was ≤37 U/ml [15]. Red cell phenotyping for Lewis antigen status was not performed in majority of the patients; there-fore, patients, whose CA19-9 levels were persistently <1 U/ml, were assumed to be Lewis antigen negative (Lea−b−) and were defined as having undetectable levels [6].

Data collection

The following data were analyzed for individual patients: age, gender, Eastern Cooperative Oncology Group performance status (ECOG PS), primary tumor site (colon or rectum), met-astatic sites, prior colectomy, histological subtypes [well-dif-ferentiated adenocarcinoma (wel), moderately differentiated adenocarcinoma (mod), poorly differentiated adenocarcinoma (por), mucinous carcinoma (muc), or signet ring cell carci-noma (sig)], baseline WBC count, baseline serum ALP level, baseline serum lactate dehydrogenase (LDH) level, base-line serum carcinoembryonic antigen (CEA) level, baseline

serum CA19-9 level, KRAS/BRAF mutation status in tumor tissue, survival status, and date of last follow-up or death. To detect point mutations in KRAS codons 12 and 13, as well as the V600E mutation in the BRAF gene, we used the cycleave PCR technique [24]. The PCR reactions were performed using a cycleave PCR core kit (TAKARA, Co. Ltd., Ohtsu, Japan). Fluorescent signals were quantified using the Smart Cycler system (SC–100; Cepheid, Sunnyvale, CA, USA).

Treatments

The details of the treatment schedule are presented in Sup-plementary Data. Patients received a FOLFOX-4, modified FOLFOX-6, or CapeOX chemotherapy regimen [1, 5, 17]. Further, patients treated with bevacizumab [5, 17], cetuxi-mab [14], and cediranib (AZD2171) [18] were included in this study. Bevacizumab has been approved for mCRC since April 2007 in Japan.

Statistical analyses

We divided patients into two groups (elevated or normal CA 19-9 levels) on the basis of their baseline CA19-9 levels and evaluated the relationship between CA19-9 levels and clin-icopathological factors using chi-squared (χ2) or Fischer’s exact tests. We excluded patients with undetectable CA19-9 levels. Overall survival (OS) was defined as the time inter-val between first-line chemotherapy and death from any cause. Survival status was updated in December 2012. Survival curves were constructed using the Kaplan–Meier method. The Cox proportional hazards model was used to evaluate the association between clinicopathological fac-tors and survival. Univariate analyses were used to evaluate the following baseline clinicopathological characteristics as potential prognostic factors [19]: age (≤70 vs. >70 years); gender (female vs. male); ECOG PS (0, 1 vs. 2, 3); primary tumor site (colon vs. rectum); number of metastatic sites (1 vs. ≥2); liver involvement (no vs. yes); prior colectomy (no vs. yes); histological subtypes (wel/mod vs. por/sig/muc); WBC count (<10,000 vs. ≥10,000/μl); ALP levels (<300 vs. ≥300 IU/l); LDH levels (≤230 vs. >230 IU/l); CEA lev-els (≤50 vs. >50 ng/ml); and CA19-9 levels (>1, ≤37 vs. >37 IU/ml). A multivariate analysis using Cox proportional hazards model was performed to assess the relationship between clinicopathological variables and survival.

To assess whether baseline CA19-9 is a prognostic marker independent of bevacizumab treatment and whether it pre-dicts the patients’ response to bevacizumab, we separated patients into four groups on the basis of whether they under-went bevacizumab treatment and whether baseline CA19-9 levels were normal or elevated. We excluded the patients treated with cetuximab/cediranib from this analysis. We also assessed the relationship between baseline CEA and OS.

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Results were considered statistically significant when the two-sided P value was <0.05. The statistical analyses were performed using R software version 2.13.2 (R Project for Statistical Computing, Vienna, Austria).

Results

Patient characteristics

Patient characteristics are summarized in Table 1. Three hundred and sixty-seven mCRC patients were treated at our institution between January 2005 and December 2009, with 252 meeting our eligibility criteria. The median fol-low-up duration was 23.3 months. No patients died within

Table 1 Patient characteristics

Characteristics N = 252

No. (%)

Age, years

Median (range) 61.0 (23–85)

Gender

Female 97 (38.5)

Male 155 (61.5)

ECOG PS

0 114 (45.2)

1 119 (47.2)

2 17 (6.8)

3 2 (0.8)

Disease status

Unresectable 124 (49.2)

Recurrent 128 (50.8)

Primary site

Colon 148 (58.7)

Rectum 104 (41.3)

Number of metastatic sites

1 116 (46.0)

≥2 136 (54.0)

Metastatic sites

Liver 118 (46.8)

Lung 146 (57.9)

Lymph node 153 (60.7)

Peritoneum 193 (76.6)

Prior colectomy

Yes 210 (83.3)

No 42 (16.7)

Histological subtypes

Wel 55 (21.8)

Mod 166 (65.9)

Por 22 (8.7)

Muc 5 (2.0)

Sig 4 (1.6)

Chemotherapy

First-line

FOLFOX/CapeOXa 133 (52.8)

FOLFOX/CapeOXa + bevacizumab 101 (40.0)

FOLFOX/CapeOXa + cetuximab 8 (3.2)

FOLFOX/CapeOXa ± AZD2171 10 (4.0)

Second-line 190 (75.4)

Third-line 99 (39.3)

WBC (/μl)

<10,000 237 (94.0)

≥10,000 15 (6.0)

ALP (IU/l)

<300 128 (50.8)

≥300 124 (49.2)

Table 1 continued

Characteristics N = 252

No. (%)

LDH (IU/l)

<230 143 (56.7)

≥230 109 (43.3)

CEA (ng/ml)

≤50 159 (63.1)

>50 93 (26.9)

CA19-9

Normal (>1, ≤37 IU/ml) 79 (31.3)

High (>37 IU/ml) 150 (59.5)

Undetectableb (≤1 IU/ml) 23 (9.2)

KRAS/BRAF status

KRAS mutant

G12X 34 (13.5)

G13X 10 (4.0)

BRAF mutant

V600E 7 (2.8)

KRAS wild type/BRAF wild type 76 (30.5)

NA 124 (49.2)

Outcome

Median follow-up [range (months)] 23.3 (1.4–86.5)

30-day mortality 0 (0)

Death 197 (78.2)

Censored 55 (21.8)

ALP alkaline phosphatase, CA19-9 carbohydrate antigen 19-9, CEA carcinoembryonic antigen, ECOG Eastern Cooperative Oncology Group, LDH lactate dehydrogenase, Mod moderately differentiated adenocarcinoma, Muc mucinous carcinoma, NA not available, Por poorly differentiated adenocarcinoma, PS performance status, Sig signet ring cell carcinoma, WBC white blood cell count, Wel well- differentiated adenocarcinomaa FOLFOX: FOLFOX-4 or modified FOLFOX-6 (fluorouracil + leucovorin + oxaliplatin)b Undetectable: Lewis antigen negative (Lea−b−)

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30 days of treatment initiation, and 197 patients died when the records were retrospectively reviewed. Seventy-nine patients had normal CA19-9 levels, 150 patients had elevated CA19-9 levels, and 23 patients had undetectable CA19-9 levels. Thirty-four patients had a KRAS G12 muta-tion, 10 patients had a KRAS G13 mutation, 7 patients had a BRAF mutation, 76 patients had wild-type KRAS and BRAF mutations, and 124 patients had unknown KRAS and BRAF genotypes.

Association of CA19-9 levels with clinicopathological factors

Table 2 shows that elevated baseline CA19-9 levels were significantly associated with liver involvement; increased

Table 2 Correlations between baseline CA19-9 and clinicopathological factors

Baseline CA19-9 value P value

Normala Highb

N = 79 N = 150

No. (%) No. (%)

Age, years

<70 64 (81.0) 120 (80.0) 0.8545

≥70 15 (19.0) 30 (20.0)

Gender

Female 24 (30.4) 62 (41.3) 0.1037

Male 55 (69.6) 88 (58.7)

ECOG PS

0, 1 76 (96.2) 139 (92.7) 0.2884

≥2 3 (3.8) 11 (7.3)

Primary site

Colon 41 (51.9) 93 (62.0) 0.1403

Rectum 38 (48.1) 57 (38.0)

Number of metastatic sites

1 42 (53.2) 64 (42.7) 0.1299

≥2 37 (46.8) 86 (57.3)

Metastatic sites

Liver

Yes 32 (40.5) 93 (62.0) 0.0019

No 47 (59.5) 57 (38.0)

Lung

Yes 25 (31.6) 54 (36.0) 0.5099

No 54 (68.4) 96 (64.0)

Lymph node

Yes 31 (39.2) 45 (30.0) 0.1581

No 48 (60.8) 105 (70.0)

Peritoneum

Yes 17 (21.5) 33 (22.0) 0.9332

No 62 (78.5) 117 (78.0)

Prior colectomy

Yes 67 (84.8) 123 (82.0) 0.5907

No 12 (15.2) 27 (18.0)

Histological subtypes

Wel/mod 68 (86.1) 131 (87.3) 0.7886

Por/muc/sig 11 (13.9) 19 (12.7)

WBC (/μl)

≤10,000 78 (98.7) 138 (92.0) 0.0380d

>10,000 1 (1.3) 12 (8.0)

ALP (IU/l)

<300 48 (60.8) 68 (45.3) 0.0265

≥300 31 (29.2) 82 (54.7)

LDH (IU/l)

<230 60 (75.9) 68 (45.3) <0.0001

≥230 19 (24.1) 82 (54.7)

Table 2 continued

Baseline CA19-9 value P value

Normala Highb

N = 79 N = 150

No. (%) No. (%)

CEA (ng/ml)

≤50 71 (89.9) 74 (49.3) <0.0001

>50 8 (10.1) 76 (50.7)

KRAS status

Mutationc 6 (14.6) 35 (50.0) 0.0002

Wild 35 (85.4) 35 (50.0)

BRAF status

Mutation 0 (0) 7 (16.7) 0.0148d

Wild 34 (100) 35 (83.3)

Chemotherapy

First-line

FOLFOX/CapeOXe 42 (53.2) 78 (52.0) 0.6748

FOLFOX/CapeOXe + bevacizumab

30 (37.9) 63 (42.0)

Second-line

Yes 54 (68.4) 117 (78.0) 0.1106

No 25 (31.6) 33 (22.0)

ALP alkaline phosphatase, CA19-9 carbohydrate antigen 19-9, CEA carcinoembryonic antigen, ECOG Eastern Cooperative Oncology Group, LDH lactate dehydrogenase, Mod moderately differentiated adenocarcinoma, Muc mucinous carcinoma, Por poorly differentiated adenocarcinoma, PS performance status, Sig signet ring cell carci-noma, WBC white blood cell count, Wel well-differentiated adenocar-cinomaa Normal: baseline CA19-9 value 1–37 IU/mlb High: baseline CA19-9 value >37 IU/mlc KRAS mutant: KRAS G12X and G13X mutationd Fisher’s exact teste FOLFOX: FOLFOX-4 or modified FOLFOX-6 (fluorouracil + leucovorin + oxaliplatin)

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WBC count; increased ALP, LDH, and CEA levels; and KRAS/BRAF mutations (P < 0.05 for all).

Prognostic value of CA19-9

The median OS was 36.7 months [95 % confidence inter-val (CI) 29.7–51.6 months] in the normal CA19-9 group, 19.8 months (95 % CI 17.0–24.4 months) in the ele-vated CA19-9 group, and 13.2 months (95 % CI 10.4–32.5 months) in the undetectable CA19-9 group. Com-pared with the normal CA19-9 group, the univariate hazard ratio (HR) for OS was 2.31 (95 % CI 1.65–3.24) for the elevated CA19-9 group (Supplementary Figure 1). Eight variables were identified as prognostic factors (ECOG PS; number of metastatic sites; peritoneal involvement;

histological subtypes; and ALP, LDH, CEA, and CA19-9 levels) (P < 0.05 for all, Table 3). Five of these signifi-cantly predicted OS: ECOG PS; number of metastatic sites; histological subtypes; LDH levels; and CA19-9 lev-els (P < 0.05 for all, Table 3). In the patients treated with bevacizumab as well as those without, CA19-9 levels were significantly associated with OS; median 36.5 months for the normal versus 27.8 months for the elevated group in FOLFOX/CapeOX plus bevacizumab treatment (HR 1.84, 95 % CI 1.03–3.28, P = 0.0382) (Supplementary Fig-ure 2A); and median 38.0 months for the normal versus 15.3 months for the elevated group in FOLFOX/CapeOX alone (HR 2.88, 95 % CI 1.84–4.51, P < 0.0001) (Supple-mentary Figure 2B). CEA levels tended to be associated with OS (Supplementary Data).

Table 3 Univariate and multivariate analysis for overall survival

ALP alkaline phosphatase, CA19-9 carbohydrate antigen 19-9, CEA carcinoembryonic antigen, ECOG Eastern Cooperative Oncology Group, LDH lactate dehydrogenase, Mod moderately differentiated adenocarcinoma, Muc mucinous carcinoma, Por poorly differentiated adenocarcinoma, PS performance status, Sig signet ring cell carcinoma, WBC white blood cell count, Wel well-differentiated adenocarcinomaa Baseline CA19-9 value 1–37 IU/mlb Baseline CA19-9 value >37 IU/ml

Variables Class Univariate analysis Multivariate analysis

HR 95 % CI P HR 95 % CI P

Age, years <70 1.00

≥70 0.98 0.68–1.42 0.92

Gender Female 1.00

Male 0.81 0.60–1.10 0.1811

ECOG PS 0, 1 1.00

≥2 4.53 2.61–7.87 <0.0001 3.01 1.69–5.36 0.0002

Primary site Colon 1.00

Rectum 1.01 0.75–1.36 0.9403

Number of metastatic sites 1 1.00

≥2 1.64 1.22–2.21 0.0012 1.66 1.22–2.24 0.0011

Liver involvement Yes 1.11 0.88–1.49 0.4806

No 1.00

Lung involvement Yes 1.05 0.77–1.43 0.7465

No 1.00

Lymph node involvement Yes 0.99 0.72–1.36 0.9379

No 1.00

Peritoneum involvement Yes 1.44 1.01–2.04 0.0427

No 1.00

Prior colectomy Yes 0.81 0.56–1.17 0.2637

No 1.00

Histological subtypes Wel/mod 1.00

Por/muc/sig 1.83 1.20–2.78 0.0047 1.89 1.24–2.88 0.0032

WBC (/μl) ≤10,000 1.00

>10,000 1.45 0.78–2.66 0.2373

ALP (IU/l) ≤300 1.00

>300 1.61 1.20–2.17 0.0015

LDH (IU/l) ≤230 1.00

>230 2.47 1.82–3.34 <0.0001 1.88 1.35–2.61 0.0002

CEA (ng/ml) ≤50 1.00

>50 1.75 1.30–2.36 0.0003

CA19-9 (IU/l) ≤37a 1.00

>37b 2.30 1.65–3.24 <0.0001 1.75 1.22–2.50 0.0021

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Predictive value of CA19-9 levels

Patients with elevated CA19-9 levels significantly benefited from bevacizumab treatment in terms of OS, as the median OS was 27.8 months in the treated group and 15.3 months in the untreated group (adjust HR 0.65, 95 % CI 0.45–0.93, P = 0.0198, Supplementary Figure 3A). However, no significant difference was found in patients with normal CA19-9 levels treated with bevacizumab, as the median OS was 38.0 months in the untreated group versus 36.5 months in the treated group (adjust HR 1.31, 95 % CI 0.62–2.74, P = 0.4825, Supplementary Figure 3B). Figure 1 shows the OS in four groups according to the addition of bevaci-zumab and CA19-9 levels at baseline. On the other hand, the patients in both the elevated and normal CEA groups tended to benefit from the addition of bevacizumab treat-ment (Supplementary Data). We summarized the patients characteristics of 4 groups according to use of bevacizumab and CA19-9 level in Supplementary Table.

Discussion

Our study indicated three major findings. First, baseline CA19-9 levels were a prognostic factor for mCRC patients. Second, serum baseline CA19-9 levels predicted the sur-vival in patients treated with chemotherapy plus beva-cizumab. Finally, elevated baseline CA19-9 levels were significantly associated with KRAS and BRAF mutations.

These results support that we should measure CA19-9 lev-els before first-line chemotherapy administration with bev-acizumab for patients with mCRC.

Our study indicates that CA19-9 is an independent prog-nostic factor for mortality in mCRC patients. CA19-9 is a cell surface glycoprotein and is involved in cellular adhe-sion. Cancer cells expressing this protein may have greater metastatic and invasive potential. Moreover, CA19-9 levels remained a poor prognostic factor even after adjusting for other factors such as ECOG PS, number of metastatic sites, histological subtypes, and serum LDH levels. Our results concur with previous reports showing that CA19-9 levels are a prognostic factor in colorectal cancer [3, 4]. Unlike our study, the patients in these studies were not treated with bevacizumab [4], a standard chemotherapy drug. This study showed that CEA levels were not a significant prognostic factor in the multivariate analysis, suggesting that CA19-9 levels may be a stronger and more independent prognostic factor than CEA levels.

To the best of our knowledge, this is the largest study to show that bevacizumab treatment increases survival in individuals with elevated CA19-9 levels, which suggests these levels could predict survival in bevacizumab-treated patients. Although it is unclear why bevacizumab treat-ment does not improve survival in patients with normal CA19-9 levels, our results concur with those of a previous report with a very small number of subjects [3]. Resistance to tumor hypoxia may be a feature of malignant cancer cells [20]. Hypoxia inducible factor-1 (HIF-1) can activate

Fig. 1 Overall survival (OS) of 214 patients treated with oxaliplatin-based chemotherapy divided into 4 groups: without bevacizumab/normal CA19-9 (solid line), without bevaci-zumab/high CA19-9 (dashed line), with bevacizumab/normal CA19-9 (dotted line), and with bevacizumab/high CA19-9 (dashed-dotted line)

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VEGF gene expression, and a previous study reported that hypoxia significantly increased sialyl Lewis A expression in colorectal cancer cells [12], which thereby increases the expression of these carbohydrate determinants in the can-cer cells. Bevacizumab, a VEGF-A inhibitor, showed sig-nificant efficacy in large clinical trials [5, 17], although our study showed that survival only improved in patients with elevated CA19-9 levels.

This is also the first report to suggest that both KRAS and BRAF mutations in tumor tissue are associated with ele-vated CA19-9 levels. A previous study indicated that serum KRAS gene mutation status was significantly associated with preoperative CA19-9 levels [22], but the relationship between circulating KRAS status and tissue KRAS status remains unclear. In contrast, we assessed the KRAS/BRAF mutation status in tumor tissue. However, the KRAS/BRAF status was only available in 128 patients (50.7 %), and BRAF mutations were only found in seven patients. There-fore, the degree to which our results can be generalized to a larger group of patients is unclear.

There were several limitations in this study. First, patients with a CA19-9 levels ≤1 U/ml were excluded from the analysis [6] and assumed to be Lewis antigen negative (Lea−b−). Second, we did not account for the response rate and dosage of each chemotherapy drug. Third, patients treated with cetuximab and cediranib were included in this study, whereas patients treated with irinotecan were excluded. Finally, the predictive value of CA19-9 levels for the benefit of bevacizumab cannot be rigorously and reliably assessed outside of a trial where patients are ran-domized to receive bevacizumab or not. Further prospec-tive studies are needed to clarify prognostic and predictive value of CA19-9 levels.

In conclusion, our study indicates that bevacizumab treatment improves survival in individuals with elevated baseline CA19-9 levels. In addition, baseline CA19-9 lev-els may help predict prognosis, bevacizumab response, and KRAS/BRAF mutation status in a clinical setting.

Conflict of interest The authors have declared no conflicts of interest.

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