Mucinous histology predicts for reduced fluorouracil responsiveness and survival in advanced colorectal cancer

F. V. Negri1, A. Wotherspoon2, D. Cunningham1,*, A. R. Norman3, G. Chong1 and P. J. Ross1

1 Department of Medicine, 2 Department of Histopathology, 3 Department of Computing and Information, Royal Marsden Hospital, London and Sutton, Surrey, UK

* Correspondence to: Prof. D. Cunningham, Department of Medicine, Royal Marsden Hospital, Downs Road, Sutton, Surrey SM2 5PT, UK. Tel: +44-208-661-3156; Fax: +44-208-643-9414; Email: david.cunningham{at}icr.ac.uk


    Abstract
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Response and survival
 Discussion
 References
 
Background:: Mucinous carcinoma of the colon and rectum (mucinous CRC) is a histological subtype of colorectal adenocarcinoma for which there is little data on chemotherapy responsiveness. The purpose of this study was to investigate specifically the efficacy of fluorouracil-based first-line chemotherapy in patients with advanced mucinous CRC.

Patients and methods:: All patients with advanced mucinous CRC enrolled in three prospective randomized trials evaluating infused 5-fluorouracil as first-line treatment were compared with patients with non-mucinous subtypes enrolled in the same trials in a case–control study. Prognostic factors associated with overall response rate (ORR), progression-free survival (PFS) and overall survival (OS) were identified using univariate and multivariate logistic and/or Cox proportional hazards analyses.

Results:: The study included 135 patients (45 cases and 90 controls). The response rates for cases and controls were 22% [95% confidence interval (CI), 11% to 38%] and 47% (95% CI, 36.1% to 58.2%), respectively (P=0.0058). Median OS for the mucinous CRC patients was 11.8 months (95% CI, 8.87–14.8) compared with 17.9 months (95% CI, 13.38–22.39) in the control group (univariate analysis, P=0.056); after correcting for significant prognostic factors by multivariate Cox regression analysis, P=0.0372 and hazard ratio (HR)=1.497 (1.02–2.19).

Conclusion:: Patients with advanced mucinous CRC have a poorer response to fluorouracil-based first-line chemotherapy and reduced survival compared with patients with non-mucinous CRC.

Key words: colorectal cancer, 5-fluorouracil, mucinous


    Introduction
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Response and survival
 Discussion
 References
 
Mucinous adenocarcinoma is one of the histological subtypes of colorectal cancer first described by Parham in 1923 [1Go]. It accounts for 5–15% of all primary colorectal cancer and is defined as a tumour with >50% of its body showing a mucinous pattern on histological examination, and with a large amount of extracellular mucin produced by secreting acini [2Go, 3Go]. This is distinct from signet-ring adenocarcinoma, a rare variant in which mucin remains inside the cell, which is well known for its aggressiveness [4Go].

It has been suggested that mucinous adenocarcinoma behaves differently from more common histological subtypes of colorectal cancer; however, its clinical implications remain unclear. According to published series, mucinous carcinoma affects younger patients, is more frequent in the proximal part of the colon and tends to present at a more advanced stage [5Go, 6Go]. Indeed, recent molecular biology studies have shown characteristic features of mucinous carcinoma (i.e. lower expression of p53, more frequent DNA replication errors expressed as microsatellite instability, specific codon 12 K-ras mutations) and, when ploidy has been determined, a higher index of diploidy was found than for non-mucinous carcinoma [7Go–11Go]. A poor prognosis has been reported by most studies, but some failed to show a correlation with prognosis or found a prognostic significance only for certain subgroups [2Go, 3Go, 12Go]. However, these series studied prognosis from diagnosis, generally in patients managed with surgery alone rather than with chemotherapy.

Fluoropyrimidine-based chemotherapy remains the standard treatment for advanced CRC. While response rates and overall survival duration have improved with modern combinations, there is a paucity of data comparing outcomes in patients with mucinous and non-mucinous histology [13Go, 14Go]. Reports of prognostic, clinical and epidemiological differences, together with the preliminary reports about differences in genetic features, suggest that mucinous CRC is a distinct biological entity behaving differently from the more common non-mucinous CRC. This raises the possibility that the efficacy of fluorouracil-based chemotherapy may differ in patients with mucinous and non-mucinous CRCs.

To examine this possibility we specifically investigated the efficacy of fluorouracil-based first-line chemotherapy in patients with advanced colorectal cancer.


    Patients and methods
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Response and survival
 Discussion
 References
 
The study group consisted of all patients with mucinous colorectal cancer (mCRC) enrolled into three consecutive prospective randomized controlled trials at the Royal Marsden Hospital, London, between April 1992 and August 1998. All three trials were approved by the ethics committee, and all patients provided written informed consent. These trials assessed first-line infused 5-fluorouracil (5-FU) in patients with advanced colorectal cancer and had broadly similar eligibility criteria. All patients had a planned maximum treatment period of 6 months. Those with responding or stable disease at the end of 6 months were observed off treatment. Results from all three studies have been reported previously [15Go–17Go]. For each case, two controls with advanced non-mucinous colorectal cancer were randomly chosen from the same database. Controls were matched for date of randomization and arm of the trial in this order of priority. Histopathological slides from all patients (cases and controls) were reviewed (A.W.). No patients with signet-ring cells or borderline features (<50% extracellular mucin) were included in the study.

Data of cases and controls were obtained using original trial records prospectively recorded and the following parameters were examined: histology (defining cases and controls), age, gender, site of primary tumour, previous adjuvant treatment, site of advanced disease, number of metastatic sites, Eastern Cooperative Oncology Group performance status (PS), baseline carcinoembryonic antigen (CEA) level, date of randomization (matched), arm of the trial (matched), number of cycles, response to treatment, reasons for premature treatment cessation, date of progressive disease and number of patients who underwent second-line treatment. Date of death or last follow-up and cause of death were updated for this analysis. Response to chemotherapy was evaluated according to the WHO criteria [18Go] Radiological reassessment was performed at 12 weeks and treatment continued in patients with stable disease to a total of 24 weeks when reassessment was repeated.

Primary tumours were classified as right-sided tumours (arising in the caecum, ascending colon or hepatic flexure), tumours arising in the transverse colon, left-sided tumours (arising in the descending or in the sigmoid colon) and tumours arising in the rectum or rectosigmoid junction. Follow-up was maintained until death.

Statistical analysis
The study design was a retrospective case–control study and the case-to-control ratio was 1:2. The two groups were compared using 2 x 2 tables for binary factors (cases versus controls, locally advanced (LAD) versus metastatic, PS 0–1 versus PS ≥2, age <60 years versus age ≥60 years, responders to first-line therapy versus non-responders and single-agent 5-FU versus fluorouracil-based combination) using the {chi}2 test, with Fisher's exact test used where appropriate. The Kaplan–Meier method was used to estimate survival (death from any cause) and progression-free survival (PFS) curves (time to progression or death) and the log-rank test was used to compare the curves. Survival and time to events were measured from the date of randomization for all patients.

Hazard ratios (HRs) for both univariate and multivariate analysis were calculated using the Cox proportional hazards model. The significance level for all analyses was 0.05.


    Results
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Response and survival
 Discussion
 References
 
Between April 1992 and August 1998, 613 patients with advanced colorectal cancer were enrolled into three consecutive prospective randomized controlled trials assessing first-line infused 5-FU-based regimens. Forty-five patients (7%) had a histologically confirmed diagnosis of invasive mucinous CRC. The 90 control patients with advanced non-mucinous CRC were matched for the date of randomization as well as for the arm of the trial. Patient characteristics of both the study and control group are shown in Table 1.


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Table 1. Patient characteristics

 
The median age was 59 years (range 16–79 years) for the study group and 62 years (range 33–80 years) for the control group; this difference was not significant (P=0.424). The distribution for location showed an increased incidence of mucinous tumours in the right colon (38% compared with 24%, P=0.107). Four percent of the patients in the mucinous group had multiple primary tumours. One patient in the control group had synchronous colorectal cancer. The majority of patients in both groups had moderately differentiated adenocarcinoma (71% versus 81% in the study and control group, respectively). Twenty-two percent of patients with mucinous CRC and 18% of patients in the study group had poorly differentiated adenocarcinoma. The difference was not statistically significant (P=0.456).

Forty-four per cent of patients with mucinous CRC and 37% of the control group had two or more metastatic sites (P=0.383). The peritoneum was the most common metastatic site in patients with mucinous CRC (44%), but nodal and liver metastases were noted in 31% and 40% of patients, respectively. Non-mucinous tumours were associated with a lower proportion of patients with nodal metastases (13%, P=0.014) and peritoneal metastases (21%, P=0.005). The most common site of metastases for patients with non-mucinous histology was the liver (63%).

Chemotherapy
Patients were matched for the date of randomization and arm of the trial to correct for differences in treatment. One-third of patients were treated with infused 5-FU alone (31%). 5-FU combined with either mitomycin C or interferon-{alpha} was administered to 69% of patients. The mean number of administered courses of first-line chemotherapy was 19 cycles in the study group and 21 in the control group. Treatment was stopped prematurely in 36% of mucinous CRC patients compared with 24% in the control group (P=0.48). Reasons for stopping treatment were progressive disease in 27% of patients with mucinous CRC and 16% of patients in the control group, patient request in 2% of mucinous CRC patients compared with 1% of controls, and toxicity in 7% of mucinous CRC patients compared with 6% of controls (P=0.26).


    Response and survival
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Response and survival
 Discussion
 References
 
Nine patients (7%) had non-evaluable disease for response assessment (four in the mucinous group and five in the control group). Table 2 shows the response rates achieved with 5-FU-based first-line chemotherapy. In the mucinous CRC group, 32% of patients experienced disease progression while on chemotherapy. One patient achieved a complete response and eight patients achieved a partial remission. Therefore the overall response rate in the study group was 22% [95% confidence interval (CI), 11% to 38%]. The overall response rate in the control group was 47% (95% CI, 36.1% to 58.2%), including nine patients (11%) who had a complete response (P=0.0058). On multivariate analysis, PS 0–1 [risk ratio 4.085 (95% CI, 1.253–13.317), P=0.02], less than two metastatic sites [risk ratio 2.296 (95% CI, 1.023–5.150) P=0.044] and non-mucinous histology [risk ratio 3.352 (95% CI, 1.379–8.149) P=0.008] were found to be independent prognostic factors for response to chemotherapy. Twenty-one patients in the study group (47%) and 41 in the control group (45%) received second-line treatment (Table 3).


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Table 2. Response rate

 

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Table 3. Number of patients receiving second-line therapy according to histology

 
Median DFS for mucinous CRC patients was 5.8 months (95% CI, 4.08–7.55) compared with 7.6 months (95% CI, 6.44–8.7) in the control group (P=0.24) (Figure 1). The hazard ratio (HR) for risk of progression for patients with mucinous CRC compared with controls was 0.81 (95% CI, 0.55–1.18).



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Figure 1. Progression-free survival for patients with mucinous colorectal cancer and matched controls.

 
With a median follow-up of 6.4 years the median OS for the mucinous CRC patients was 11.8 months (95% CI, 8.87–14.8) compared with 17.9 months (95% CI, 13.38–22.39) in the control group (on univariate analysis, P=0.056) (Table 4 and Figure 2). The 1-year OS was 44.4% (95% CI, 29.7% to 58.2%) for the mucinous group compared with 61.1% (95% CI, 50.2% to 70.3%) for the non-mucinous group. Peritoneal disease, although more frequent in patients with mucinous CRC, did not influence OS on univariate analysis (P=0.237). After correcting for significant prognostic factors by multivariate Cox regression analysis, mucinous differentiation was associated with poorer OS [P=0.0372, HR = 1.497 (95% CI, 1.02–2.19)] (Table 5). Other significant prognostic factors for OS were PS, tumour site, CEA and number of metastatic sites.


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Table 4. Univariate analysis of overall survival following first-line treatment with 5-FU-based regimens

 


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Figure 2. Overall survival for patients with mucinous colorectal cancer and matched controls.

 

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Table 5. Multivariate analysis of overall survival following first-line treatment with 5-FU-based regimens

 

    Discussion
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Response and survival
 Discussion
 References
 
Conflicting results are found in the published literature regarding the relationship between mucinous colorectal cancer and survival. Although the weight of the published literature suggests that mucinous adenocarcinoma is associated with poorer outcome, contradictory reports suggest that the clinical relevance of this histological type in this patient population remains unclear [3Go, 12Go, 19Go]. The lack of consensus may be attributable to the limited detection power inherent in studies that test small subsets of patients and the diversity inherent in the inclusion of patients with all Dukes’ stages in the analysis. Indeed, these series studied prognosis from initial diagnosis, generally in patients managed with surgery alone, and did not specifically address outcomes in patients treated with chemotherapy. Therefore published data on the responsiveness of mucinous CRC to chemotherapy are lacking.

This case–control study shows that mucinous CRC is less responsive to 5-FU-based chemotherapy than non-mucinous adenocarcinomas. On univariate and multivariate analyses histology, together with PS and number of metastatic sites, was found to be significantly predictive of response to treatment. Furthermore, we showed significantly worse overall survival for patients with advanced mucinous CRC on multivariate analysis (P=0.0372).

Although this analysis is subject to the limitations of a case–control study, we utilized data from prospective randomized trials, each of which studied similar patient populations with infused 5-FU-based chemotherapy. In order to minimize bias further, randomly selected controls were matched for treatment arm and date of initial randomization. This rigorous study design reinforces our findings.

Mucinous tumours were associated with a higher proportion of patients with nodal metastases (31%, P=0.04) and peritoneal metastases (44%, P=0.005), while the most common site of metastases for patients with non-mucinous histology was the liver (63%). However, these imbalances do not explain the effect on survival. A higher proportion of peritoneal metastases in patients with mucinous CRC was also reported in previous studies [6Go, 12Go, 19Go]. Conversely, in the present study, the other main characteristics of patients, such age, performance status, primary tumour side, baseline CEA level and number of metastatic sites, were comparable in cases and controls.

The significant difference in the 5-FU sensitivity of mucinous CRC compared with non-mucinous carcinoma, as shown here, raises the possibility that therapeutic benefit may be largely reduced in this histological subtype. Microsatellite instability (MSI) appears to occur more frequently in mucinous than in non-mucinous CRC [9Go]. In vitro, colon cancer cell lines displaying high-frequency MSI are less responsive to 5-FU than microsatellite stable cell lines [20Go]. In addition, a recent study showed that adjuvant chemotherapy with 5-FU benefited patients with tumours exhibiting chromosomal instability, but not those with microsatellite instability [21Go]. However, the predictive value of MSI for treatment response in mucinous CRC remains to be determined. Investigating mucinous CRC as a separate entity is challenging, mainly because the rarity of the disease limits the power to detect statistically significant differences in survival between subgroups. The experience at RMH suggests that the proportion of patients with advanced mucinous CRC treated on clinical trials is <10%.

Recent molecular studies support the hypothesis that mucinous CRC represents a biologically distinct entity. The analysis of the peculiarities of mucinous tumours has led to the hypothesis that there is a ‘mucinous pathway of carcinogenesis’ leading to the emergence of the mucinous phenotype [22Go]. These tumours are characterized by frequent and strong expression of the MUC2 gene and a higher frequency of K-ras mutations than non-mucinous carcinomas [23Go–25Go]. In contrast, the frequency of DCC gene loss and mutations in the p53 gene is lower in mucinous than in non-mucinous colonic carcinomas [7Go, 26Go, 27Go]. Similar findings were associated with the development of mucinous carcinomas of the breast, ovary and pancreas [28Go–30Go]. These observations suggest that perhaps we should base our treatments on the molecular characteristics of tumours rather than their organ of origin [31Go].

A current challenge is to define the biological characteristics of colon tumour cells resistant to chemotherapy. For example, in a recent published study it has been shown that the differential expression of mucins in human colon cancer cells is related to their specific resistance to anticancer drugs [32Go]. In particular, the clone resistant to 5-FU mainly produced MUC2, the mucin associated with the mucinous carcinoma subtype of colon carcinoma. Interestingly, the clone resistant to 5-FU was very sensitive to methotrexate. Therefore it is tempting to speculate that mucins may play a role in the resistance of tumour cells to chemotherapy, although the precise nature of this role is not clear.

In conclusion, our data suggest that mucinous CRC is characterized by relative resistance to 5-FU chemotherapy and reduced overall survival. The mechanism of this resistance is unknown and requires further investigation. Microarray gene expression profiling may enhance the prediction of tumour response to chemotherapy and provide further insights into the characterization of mucinous CRC.

Received for publication December 24, 2004. Revision received March 10, 2005. Accepted for publication March 11, 2005.


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 Introduction
 Patients and methods
 Results
 Response and survival
 Discussion
 References
 
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