BMJ  2004;328:382 (14 February), doi:10.1136/bmj.37972.497234.44 (published 29 January 2004)

Paper

Patients' preferences for the management of non-metastatic prostate cancer: discrete choice experiment

¹ Centre for Health Economics, University of York, Heslington, York YO10 5DD, ² Health Economics Facility, Health Services Management Centre, University of Birmingham, Birmingham B15 2RT, ³ Institute of Urology, Royal Free and University College Medical School, London W1P 7PN, ⁴ Meyerstein Institute of Oncology, Middlesex Hospital, London W1T 3AA

Abstract

Objective To establish which attributes of conservative treatments for prostate cancer are most important to men.

Design Discrete choice experiment.

Setting Two London hospitals.

Participants 129 men with non-metastatic prostate cancer, mean age 70 years; 69 of 118 (58%) with T stage 1 or 2 cancer at diagnosis.

Main outcome measures Men's preferences for, and trade-offs between, the attributes of diarrhoea, hot flushes, ability to maintain an erection, breast swelling or tenderness, physical energy, sex drive, life expectancy, and out of pocket expenses.

Results The men's responses to changes in attributes were all statistically significant. When asked to assume a starting life expectancy of five years, the men were willing to make trade-offs between life expectancy and side effects. On average, they were most willing to give up life expectancy to avoid limitations in physical energy (mean three months) and least willing to trade life expectancy to avoid hot flushes (mean 0.6 months to move from a moderate to mild level or from mild to none).

Conclusions Men with prostate cancer are willing to participate in a relatively complex exercise that weighs up the advantages and disadvantages of various conservative treatments for their condition. They were willing to trade off some life expectancy to be relieved of the burden of troublesome side effects such as limitations in physical energy.

Introduction

Several situations exist where patients face trade-offs between the risks and benefits of alternative therapies.¹ The conservative management of men with organ confined or locally advanced prostate cancer is such a situation. Treatment options include watchful waiting or oral steroidal or non-steroidal antiandrogen monotherapy.² Many patients choose castration, performed medically rather than surgically. Alternatively, there is the option of antiandrogen treatment combined with medical or surgical castration.

To make an informed choice, men need to weigh up the slight differences in effectiveness of treatments against their side effects. For example, non-steroidal antiandrogen monotherapy offers potential advantages over castration for impotence, loss of libido, and hot flushes, but these may be achieved at the cost of an increased risk of gynaecomastia and breast pain.³

Individuals' preferences for alternative treatments need to be considered in the light of the attributes of the treatments. Discrete choice experimentation identifies the key characteristics of alternative treatments and selects a series of levels for each (for example, absent, mild, moderate). Respondents choose from several options, each of which details a series of attributes at different levels. The relative importance of attributes to individuals, and the trade-offs made between them, can be assessed by changing the levels of the attributes and asking participants to make their choice again. We used discrete choice experimentation to elicit treatment related preferences in a sample of men with non-metastatic prostate cancer.

Methods

Pilot study
We conducted a two phase pilot study. In the first phase, 14 men were interviewed by a research nurse. On the basis of these interviews eight attributes were selected for the main study: diarrhoea, hot flushes, ability to maintain an erection, breast swelling or tenderness, physical energy, sex drive, life expectancy, and out of pocket expenses. In the second phase, nine men were asked to complete a questionnaire based discrete choice experiment with these attributes; there was also a brief unstructured interview with a research nurse. Several men needed guidance from the research nurse to complete the exercise, so we used an interview format for the main study.

Study format
The attributes and levels used in the exercise are described on bmj.com. We chose mild and moderate levels only. The mild level included symptoms that would not interfere with work, study, housework, family, or leisure activities, and the moderate level included symptoms that would.

A research fellow conducted the interviews and collected patients' personal data. The men were presented with two treatment options, each containing a set of attributes at specific levels. The interviewer read out the pair wise options and used show cards as prompts to help the men choose the options they preferred (table 1).

View this table: [in this window] [in a new window]   Table 1 Example of show card used in discrete choice experiment

 

The men had to assume a life expectancy of five years, estimated as the average for the sample considering the mean age (70 years) and clinical stage of disease. The two parts of the exercise each contained eight pair wise options. We prepared eight different versions of the questionnaire, each representing a new experimental design (orthogonal main effects). Each version of the questionnaire presented different levels of the cost attribute to allow a larger number of intervals between cost levels across the survey. Study patients were randomly allocated to one of the questionnaires.

Study sample
Our study sample was patients with non-metastatic prostate cancer who had or had never received anti-androgen therapy; there were no exclusion criteria. Potential participants were identified from hospital medical records and were asked to make an appointment for interview.

Analysis
We took each choice between pair wise options as a specific observation. Hence each respondent provided a maximum of 16 observations. Two separate models were specified, one for each group of attributes (see bmj.com for details of models). We explored the interactions between attributes and patient characteristics (age, prostate specific antigen level, and T stage of cancer at diagnosis).

Results

Between 24 May and 8 September 2000, we invited 180 men to participate in our study. Of these, 129 were interviewed. Participants were similar to those who declined for mean age and T stage at diagnosis. See bmj.com for characteristics of the participants.

Discrete choice experiment
Table 2 shows that the coefficients for the attributes in the first part of the exercise were all statistically significantly different from 0; negative values for libido, maintaining an erection, and physical energy indicate that the more severe the problems, the less likely the patient is to prefer that scenario; negative values for out of pocket expenses indicate that the higher the costs, the less likely the patient is to prefer that scenario. Positive values for life expectancy indicate that the greater the life expectancy the more likely the patient is to prefer that scenario. The only statistically significant interaction was between ability to maintain an erection and age; the positive value indicates that older men were less likely to be influenced by the ability to maintain an erection in choosing their preferred scenario.

View this table: [in this window] [in a new window]   Table 2 Results of first part of discrete choice exercise

 

Table 3 shows that the coefficients for the attributes in the second part of the exercise were all statistically significantly different from zero; negative values indicate that the more severe the problem the less likely the patient is to prefer that scenario. None of the interaction terms were statistically significantly different from zero.

View this table: [in this window] [in a new window]   Table 3 Results of second part of discrete choice exercise

 

Table 4 shows how much life expectancy the men were willing to trade off to achieve an improvement by one level in one of the other attributes. For example, men were willing to trade off 1.8 months of life expectancy to change diarrhoea from a moderate to mild level or from mild to absent. Because the levels of severity differed between attributes, marginal rates of substitution between attributes should be compared with caution. The most important marginal rates of substitution were for physical energy.

View this table: [in this window] [in a new window]   Table 4 Patients' marginal rates of substitution between life expectancy and other attributes

 

Discussion

Men with prostate cancer are willing to participate in the relatively complex exercise of discrete choice experimentation to weigh up the benefits and risks of various conservative treatments, irrespective of the stage of cancer or whether they had received such treatment. To our knowledge, our study is the first to elicit preferences from patients with prostate cancer using discrete choice experimentation, and provides further evidence that this approach can be applied successfully in health care. A novel feature of our study was the use of two groups of attributes. This allowed the choices to be kept relatively simple (maximum of six attributes), and the inclusion of a common core of two attributes (cost and life expectancy) ensured tradeoffs across all attributes.

The men were willing to trade off some life expectancy to be relieved of side effects, assuming a life expectancy of five years (the average in the group) as a starting point. The size of the trade-offs, however, should be treated with caution because men may have indicated different preferences if their actual life expectancy had been presented to them.

The results are averaged across the sample and so there is inevitable variation between the men. Therefore careful assessment of individual patient preferences in a clinical setting is needed.

Our findings could be used by clinicians to help patients choose between conservative treatments; knowing about the preferences of other men with prostate cancer might help patients to clarify their own thoughts. A common therapeutic dilemma is the timing of androgen suppression. Should a patient start therapy early, once progression of prostate cancer has been identified? Benefits might include a slowing down of disease progression and perhaps a reduced likelihood of death related to the cancer. Alternatively, treatment could be deferred for an agreed time. This would avoid the immediate side effects of treatment and possibly reduce the medium to long term adverse effects. This type of trade-off is made by many patients everyday, and discrete choice experimentation could gain some insight into the way patients make this difficult choice.

What is already known on this topic Various factors need to be considered in making treatment decisions in prostate cancer Patients' views on which factors of treatment are important to them and how they trade off these factors are under-researched What this study adds Men are willing to contemplate trading off life expectancy to be relieved of the burden of side effects such as limitations in physical energy The preferences of older men are not the same as those of younger men

---

Editorial by Ryan

Treatment attributes and levels and probit models are on bmj.com

This is the abridged version of an article that was posted on bmj.com on 29 January 2004: http://bmj.com/cgi/doi/10.1136/bmj.37972.497234.44

We thank Rob Sheldon (Accent Marketing and Research) for help with the design and analysis of the study, Wendy Coucill for her work on the pilot study, and the patients.

Contributors: See bmj.com

Competing interests: MS, SB, and ME have been paid as consultants for AstraZeneca.

Ethical approval: Local research ethics committee.

References

1. Kassirer JP, Pauker SG. The toss-up. N Engl J Med 1981;305: 1467-9.[Medline]
2. Adolfson J. The natural history of early prostate cancer and the impact of endocrine treatment. Eur Urol 1999;36(suppl 2): 3-8.
3. Iverson P, Tyrrell CJ, Kaisary AV, Anderson JB, Baert L, Tammela T, et al. Casodex (bicalutamide) 150-mg monotherapy compared with castration in patients with previously untreated nonmetastatic prostate cancer: results from two multicentre randomised trials at a median follow-up of 4 years. Urology 1998;51: 389-96.[CrossRef][Web of Science][Medline]

(Accepted 25 November 2003)

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