To the Editor: I note with interest the results of the study by Morris and colleagues comparing survival outcomes for patients with colorectal cancer treated in public and private hospitals.1

Stage of disease is a major determinant of survival in colorectal cancer, yet, as stated in their article, stage of disease was derived solely from pathology reports. I believe that this method would have very limited accuracy in diagnosing stage IV disease. Determining stage IV disease requires additional investigations such as computed tomography, which may either not have been performed before surgery, or the results of which may not have been noted on the pathology request form. Underdiagnosis of stage IV disease appears likely, as the incidence of stage IV disease of about 10% noted in this study is substantially less than the 20%–25% incidence observed in other epidemiological studies.2 Moreover, the limitations associated with the use of pathology reports to determine stage IV disease have been observed by other investigators.3

Although this study evaluates an interesting question in relation to the management of colorectal cancer, the significant possibility of an imbalance of important prognostic factors (such as tumour stage) between public and private patients creates major doubt about its conclusions.

To the Editor: We suggest that marked differences in comorbidities could be one explanation for the superior outcomes for patients with colorectal cancer treated in private hospitals as reported in the study by Morris et al.1 We also have concerns about the quality of the data used in their study.

We used a comprehensive prospective database to examine a cohort of Victorian patients treated at the Royal Melbourne Hospital (n = 260) and the adjacent Melbourne Private Hospital (n = 118) between 2003 and 2006. Specifically, we included data on important patient variables that were not considered in the Western Australian series (Box). These data showed a clear bias towards improved postoperative and long-term survival outcomes for patients in the private system, independent of cancer treatment. Significantly, diabetes, which affected a much larger proportion of public than private hospital patients, is also associated with inferior cancer-specific outcomes.2 Together, these results could explain the differences reported by Morris et al. In support of this, the 5-year cancer-specific survival rates they report for stage I cancer in the two hospital groups is similar (89% public versus 92% private), but the overall survival rates are markedly different (74% public versus 85% private) — consistent, we contend, with an excess of non-cancer deaths in public patients.

Morris et al also report an imbalance in the receipt of adjuvant chemotherapy between public and private patients, possibly a marker of inequality of care. We analysed prospectively collected data for our patients with stage III colon cancer, where adjuvant chemotherapy has a proven impact on survival. As shown in the Box, a similar percentage were offered, accepted and completed adjuvant chemotherapy, suggesting, in Victoria at least, similar access to care and support for public and private patients.

The pathology-based staging used by Morris et al may also be inaccurate, as recording of stage IV disease relies on the surgeon noting this on the pathology request form and patients having been fully evaluated before surgery (we contend that preoperative computed tomography scanning would not have been routine). This may explain the relatively low percentage of patients recorded as having stage IV disease (12% public; 9% private) compared with 17% in our combined series in which prospective clinicopathological staging was used.

Finally, inaccurate data are suggested by the reported 5-year overall survival figures for patients with stage IV cancer (17% in private care).1 That this is superior to figures reported in recent clinical trials is an unexpected finding, particularly as clinical trials enrol only a select subset of patients and provide access to novel combination chemotherapy, and presentation with metastatic disease is an adverse prognostic factor.

In reply: The first issue is whether we accurately identified patients with stage IV disease, as the incidence in our study was only 11% and the anticipated incidence is normally 20%–25%. We agree that simply reviewing pathology reports would tend to underdiagnose stage IV disease. However, all patients were crosschecked to the linked database to see if they had had a computed tomography scan or ultrasound image showing metastatic disease. In addition, we only reviewed patients whose primary cancer was resected. This excluded about a third of all the patients with stage IV disease. In my (C P) own surgical prospective colorectal cancer database of 781 patients, (1996 to 2007), 24% of the 185 referred with colorectal cancer had stage IV disease (private hospital patients, 21% v public hospital patients, 25%). Resection of the primary cancer was only undertaken in 126 of the 185 patients with stage IV disease (68%). Therefore, only 16% of all patients with colorectal cancer who had resections had stage IV disease (126/781).

Tebbutt argues that there could be a possibility of some imbalance between public and private patients based on this observation. We argue that the difficulty in diagnosing stage IV disease applies equally to public and private patients. Similarly, my own database does not show a significant difference in the incidence of stage IV disease between public and private hospital patients.

Kosmider et al report that, at their own institution, completion rates for chemotherapy for stage III colon cancers are the same for public and private patients, “. . . suggesting, in Victoria at least, similar access to care and support for public and private patients”. These results are hardly comparable with our study. Their observations are limited to a select subgroup and only relevant to a small section of the Victorian population, where there is a collocated public and private hospital. In contrast, our study included the entire population of Western Australia, and all public and private hospital patients. Interestingly, we noted wide variations in the rates at which chemotherapy was used, not only between public and private hospitals, but also between individual hospitals. We also noted that there are few collocated public and private hospitals within WA. The fact remains that, at a population level, public hospital patients in WA were less likely to receive chemotherapy.

Finally, Kosmider et al raise the issue that comorbidities can influence overall and cancer-specific survival (especially in relation to diabetes). We recognise this as a weakness of our study, and highlighted it in the discussion. Nonetheless, we did include a number of measures of social disadvantage in the analysis. Such measures can act as surrogate markers of common comorbidities. For example, there is a fairly clear association between type 2 diabetes and disadvantage.1 We therefore do not believe that comorbidities can account for all of the observations seen in our study. Our conclusion therefore remains — that patients with colon and rectal cancer treated in private hospitals in WA had superior outcomes. In reality, given the inequities between the two systems, is this really so surprising?