What determines patient preferences for treating low risk basal cell carcinoma when comparing surgery vs imiquimod? A discrete choice experiment survey from the SINS trial

Abstract

Background: The SINS trial (Controlled Clinical Trials ISRCTN48755084; Eudract No. 2004-004506-24) is a randomised controlled trial evaluating long term success of excisional surgery vs. imiquimod 5% cream for low risk nodular and superficial basal cell carcinoma (BCC). The trial included a discrete choice experiment questionnaire to explore patient preferences of a cream versus surgery for the treatment of their skin cancer.

Methods: The self-completed questionnaire was administered at baseline to 183 participants, measuring patients' strength of preferences when choosing either alternative 'surgery' or 'imiquimod cream' instead of a fixed 'current situation' option (of surgical excision as standard practice in UK). The treatments were described according to: cost, chance of complete clearance, side effects and appearance. Participants had to choose between various scenarios. Analysis was performed using a mixed logit model, which took into account the impact of previous BCC treatment and sample preference variability.

Results: The analysis showed that respondents preferred 'imiquimod cream' to their 'current situation' or 'surgery', regardless of previous experience of BCC symptoms and treatment. Respondents were more likely to be worried about their cosmetic outcomes and side effects they might experience over and above their chance of clearance and cost. Those with no experience of surgery (compared with experience) valued more the choice of 'imiquimod cream' (£1013 vs £781). All treatment characteristics were significant determinants of treatment choice, and there was significant variability in the population preferences for all of them.

Conclusions: Patients with BCC valued more 'imiquimod cream' than alternative 'surgery' options, and all treatment characteristics were important for their choice of care. Understanding how people with a BCC value alternative interventions may better inform the development of health care interventions.

Figure 1

Example of Choice Set.

Figure 2

Modelling patient preferences: Utility values. Note: This Figure reports on average values only, whilst the complete output from the logistic regression model is presented in Tables 3 (whole sample) and 4 (subgroups with experience and with no experience of BCC symptoms and treatment). Alternative specific constants (ASC) for surgery (ASC _SURGERY) and for cream (ASC _CREAM) show the preferences of these alternatives relative to the current situation, everything else being equal. The cost attribute reported a mean value of −0.0031, and therefore it is less noticeable than the other attributes. Due to differences in scale factors across data sets, utility values from different subgroups are not directly comparable. For comparison between subgroups with experience and with no experience of BCC symptoms and treatment please see marginal WTP (Figure 3) and proportion of respondents (Figure 4). Overall findings from subgroup analyses are also presented in Table 4.

Figure 3

Modelling patient preferences: Marginal WTP values (£). Note: This Figure reports on mean values only, whilst the complete output from the logistic regression model, marginal WTP calculations (mean and standard deviation values), and their comparison between subgroups is presented in Tables 3 (whole sample) and 4 (subgroups with experience and with no experience of BCC symptoms and treatment). For ‘CHANCE’, ‘MODERATE SIDE EFFECTS’ and ‘NORMAL APPEARANCE’ differences in marginal WTP between subgroups (with experience vs. with no experience of BCC symptoms and treatment) are significant at the 95% level.

Figure 4

Modelling patient preferences: the proportion of respondents (%) with positive effect of particular characteristic. Note: The output from the logistic regression model used to inform these estimates is presented in Tables 3 (whole sample) and 4 (subgroups with experience and with no experience of BCC symptoms and treatment, and their comparison). For ‘MODERATE SIDE EFFECTS’ and ‘NORMAL APPEARANCE’ differences in preference distribution between subgroups (with experience vs. with no experience of BCC symptoms and treatment) are significant at the 95% level.