378 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2008 vol. 32 no. 4© 2008 The Authors. Journal Compilation © 2008 Public Health Association of Australia

Cancer Article

Reliability of collecting colorectal cancer stage

information from pathology reports and

general practitioners in Queensland

Interpretation of differences in cancer

survival between population subgroups

o r over t ime requi res accura te

information on cancer stage.1-3 However,

clinical stage is not routinely collected

by population-based cancer registries in

Australia or overseas. Some population-

based registries, such as the SEER program,4

EUROCARE5 and the New South Wales

cancer registry in Australia,6 report a

summary measure of stage that is based

on information from pathology reports or

medical records, however error rates between

12 and 35% for prostate, lung and breast

cancers have been reported.7-10

Collecting information on cancer stage using

resource-intensive methods such as reviews of

medical charts is not practical for large-scale

studies or population-based registries. GPs,

as the gatekeepers to more specialised cancer

services, are a potential source of information

about cancer stage, as are pathology reports.

A Western Australian study suggested that

colorectal cancer is probably the cancer most

Abstract

Objective: To investigate the reliability of

collecting colorectal stage information from

pathology reports and general practitioners

in Queensland, Australia.

Methods: A longitudinal study of colorectal

cancer survivors conducted in 2003 and

2004 (n=1966, response rate=57%)

obtained stage information from clinical

specialists (n=1334), general practitioners

(GP) (n=1417) and by extracting stage

from pathology reports (n=1484). Reliability

of stage information was determined by

comparing stage from GPs and pathology

reports with that reported by the clinical

specialists, using a weighted kappa.

Results: GPs and pathology reports each

had a similar level of agreement with

clinical specialists, with kappa scores of

0.77 (0.75-0.80) (n=1042) and 0.78 (0.75-

0.81) (n=1152), respectively. Results were

similar when restricting to records staged

by all three methods (n=847). GPs had

similar levels of agreement with clinical

specialists within each stage, although

pathology reports tended to under-stage

patients in Stage D (0.37). Collapsing

stage into two categories (A or B, C or D)

increased the reliability estimates from the

pathology reports to 0.91 (0.88-0.93), but

there was little change in GP estimates

0.79 (0.75-0.83).

Conclusions: Extractions from pathology

reports are a valid source of broad stage

information for colorectal cancer.

Implications: In the absence of clinical

stage data, access to pathology records by

population-based cancer registries enables

a more accurate assessment of survival

inequalities in colorectal cancer survival.

Aust N Z Public Health. 2008; 32:378-82

doi: 10.1111/j.1753-6405.2008.00259.x

Submitted: February 2008 Revision Requested: April 2008 Accepted: June 2008Correspondence to: Dr Peter Baade, Epidemiology Unit – Viertel Centre for Research in Cancer Control, The Cancer Council Queensland, PO Box 201, Spring Hill, Queensland 4004. Fax: 07 3258 2310; e-mail: Peterbaade@cancerqld.org.au

Lauren J. KrnjackiEpidemiology Unit, Viertel Centre for Research in Cancer Control, The Cancer Council Queensland

Peter D. BaadeEpidemiology Unit, Viertel Centre for Research in Cancer Control, The Cancer Council Queensland and School of Public Health, Queensland University of Technology

Brigid M. LynchEpidemiology Unit, Viertel Centre for Research in Cancer Control, The Cancer Council Queensland

Joanne F. AitkenEpidemiology Unit, Viertel Centre for Research in Cancer Control, The Cancer Council Queensland and School of Population Health, Queensland University

amenable to obtaining stage from pathology

reports, with the limitation that information

on metastasis is often lacking.11

A longitudinal study of colorectal cancer

survivors12 collected stage information from

pathology reports, general practitioners

and clinical specialists in Queensland.

This paper reports on the reliability of this

stage information by comparing stage from

pathology reports and general practitioners

with that of clinical specialists.

MethodData were collected as part of the

Colorectal Cancer and Quality of Life

Study, a population-based, longitudinal

study of the predictors of quality of life up

to five years after diagnosis. Full details are

described elsewhere.12 Briefly, all eligible

cases of colorectal cancer were identified

through the Queensland Cancer Registry.

Study participants had a first, histologically

confirmed, primary diagnosis of colorectal

2008 vol. 32 no. 4 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 379© 2008 The Authors. Journal Compilation © 2008 Public Health Association of Australia

cancer between 1 January 2003 and 31 December 2004, and were

aged between 20 and 80 years at diagnosis. Of 3,426 eligible

participants, 1,966 (57.4%) completed a baseline telephone

interview. The University of Queensland’s Behavioural and

Social Science Ethical Review Committee approved the study’s

procedures.

Stage information from doctorsDuring the telephone interview, participants were asked to name

their treating doctor(s), including their GP, surgeon and medical

oncologist where applicable. Questionnaires were mailed to these

doctors approximately 12 months after the participant’s diagnosis,

requesting a range of clinical information including the stage at

diagnosis (based on the Australian Clinico-Pathological Staging

(ACPS) system). The ACPS system is essentially an extension

of the traditional Dukes staging method, and is based on a small

number of key variables: direct spread, lymph node metastases,

and known residual tumour.13 Reminder letters were sent at six

and 12 weeks. If the surgeon or medical oncologist preferred,

study personnel extracted the required information from medical

records, including letters of correspondence, outpatient notes,

operative reports, chemotherapy and radiation therapy charts, at the

treating hospital or the clinician’s rooms. In these record reviews,

stage was recorded only if it was stated explicitly in the record. No

effort was made to interpret stage from the clinical information

provided. When stage information differed between surgeons and

medical oncologists, the data from surgeons was used.

Stage information from pathology reportsA research officer trained in the interpretation of colorectal

cancer pathology reports extracted stage information from

pathology reports held by the Queensland Cancer Registry.

Documentation pertaining to the time up to two months post

diagnosis was reviewed. Tumour information was extracted from

the pathology report, using the ‘Tumour, Nodes, Metastasis’

(TNM) staging system.14 In the absence of information on

metastases (MX), it was assumed that there were no metastases

(MO). This method has been used previously in the extraction

of stage from pathology reports.11 The TNM was then classified

according to Australian Clinico-Pathological Staging. The

research officer did not attempt to stage if there was any ambiguity

regarding the level of invasion of the tumour from the information

on the pathology report. The records for 50 participants were

subsequently staged by a second reviewer to assess inter-rater

reliability.

Statistical AnalysesOther studies have suggested that stage data from clinical

records are generally considered to be the best available.10,15

These analyses focused on the reliability of stage information

obtained from pathology reports and GPs compared to clinical

specialists.

Reliability was determined by comparing reported stage

from each source to that reported by the clinical specialist,

using a weighted Kappa. The weighted Kappa calculates

the chance corrected agreement between reporters, and takes

into account the magnitude of the differences in agreement.

It has been suggested that Kappa estimates between 0.4-0.6

represent ‘moderate agreement’, 0.61-0.8 ‘substantial agreement’

and 0.81-1.00 ‘almost perfect agreement’.16 Confidence intervals

for the Kappa estimates were calculated using the bootstrap

method (1000 repetitions). Kappa estimates were also stratified

by (clinical specialist-defined) stage to determine the consistency

of agreement. Per cent agreement was calculated to assist

interpretation.

Pairwise comparisons with the stage reported by clinical

specialists were carried out separately for stage reported by

GPs and stage extracted from the pathology reports. In these

comparisons, records with missing stage information were deleted.

Since these two comparisons were then based on different (albeit

overlapping) samples, we also conducted pairwise comparisons

on those records that had non-missing stage information from all

three collection methods.

We assessed the impact that collapsing stage into broader

categories had on the measured levels of reliability. Five year

survival for Stage A is approximately 88%; 70% for Stage B;

43% for Stage C; 7% for Stage D.17 This supported the collapsing

of stage into ‘Local/Locally advanced’ (Stage A and B) versus

‘Regional/Distant’ (Stage C and D).

The current Australian treatment guidelines for colorectal

cancer recommend different treatment based on the stage of the

tumour.18 Those with Stage A are typically treated with surgery

alone. Patients with Stage C and D are recommended to have

chemotherapy. There is some ambiguity regarding treatment

for patients with Stage B depending on the prognosis and site

of the tumour. This supports the grouping of stage into likely

treatment groups of ‘surgery only’ (Localised – Stage A),

‘possible chemotherapy’ (Non-localised – Stage B) and ‘at least

chemotherapy’ (Regional and Distant – Stages C and D).

ResultsReporting of stage

Approximately 94% of participants had a report of stage

available from at least one of the three data sources. There were

1,950 participants (99.2%) who reported having been treated by

a clinical specialist, and of these, stage information was obtained

for 1,417 (72.6%). This combined clinical stage information was

based on surgical stage for 95.5% of patients, and was obtained

from medical oncologists for the remaining 4.5%. When stage

information was obtained from both surgeons and medical

oncologists (n=427), agreement was very high (92% concordance).

Nearly all (97.7%) participants reported having a regular GP,

and for 1,332 (69%) of these participants we obtained stage

information from the GP.

Since an eligibility requirement for this study was to have

histologically confirmed colorectal cancer, all respondents had

a pathology report available in the Queensland Cancer Registry.

Cancer Colorectal cancer stage information

380 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2008 vol. 32 no. 4© 2008 The Authors. Journal Compilation © 2008 Public Health Association of Australia

Table 1: Comparisons between stage as provided by general practitioners and extracted from pathology reports, using the stage from clinical specialists as the comparison group.

Type of comparison Statistic Stage groups A, B, C, D A, B, C/D A/B, C/DPathology reportsAll comparisons (N=1,152)

W Kappa 0.78 (0.75-0.81) 0.83 (0.80-0.86) 0.90 (0.88-0.93)

% Agr 81.8 86.7 95.2

All three groups (n=847)

Kappa 0.79 (0.76-0.82) 0.84 (0.81-0.87) 0.91 (0.88-0.94)

% Agr 82.2 87.3 95.5

General practitionersAll comparisons (N=1,042)

Kappa 0.77 (0.75-0.80) 0.78 (0.75-0.81) 0.79 (0.75-0.83)

% Agr 79.3 84.1 89.5

All three groups (n=847)

Kappa 0.77 (0.74-0.80) 0.78 (0.74-0.81) 0.78 (0.73-0.82)

% Agr 80.4 83.7 89.1Notes:(a) Weighted Kappa – chance corrected agreement between reporters, taking into account the magnitude of the differences in agreement (include 95% confidence

interval)(b) % Agreement – proportion of exact stage agreement (c) All comparisons – when stage information available for both groups involved in the comparisons (eg. pathology extraction and clinical specialist).(d) All three groups – when stage information available for all three groups of pathology extraction, GP and clinical specialist.

Table 2: Stratification of percent agreement and Kappa by stage, comparing to stage as determined by clinical specialists.

Clinical Specialist Stage A B C DPathology reports (n = 1152)A 93.5 18.5 2.1 0.0

B 6.0 79.1 4.5 18.8

C 0.0 2.4 92.4 54.2

D 0.5 0.0 1.1 27.1

Kappa 0.73 0.74 0.82 0.38

General practitioner (n = 1,042)A 84.4 8.4 3.5 0.0

B 13.1 78.6 11.7 2.3

C 2.1 9.8 75.1 12.3

D 0.5 3.2 9.7 85.4

Kappa 0.77 0.69 0.68 0.74Notes:(a) Kappa – chance corrected agreement between reporters on each stage(b) % Agreement – proportion of exact agreement on each stage

There was sufficient information to extract stage from the

pathology record for 1,480 (75.3%) of the participants in the study.

Of the 50 pathology records that were coded separately by two

researchers, only three were different (94% agreement).

There were 1,152 records (58.5% of the total sample) available

for the pairwise comparisons between clinical specialists and

extractions from pathology reports, while 1,042 records (53.0%)

were used for the pairwise comparisons between clinical specialists

and general practitioners. A total of 847 records (43.1% of sample)

had stage information from all three sources.

There were no apparent differences in the sex (χ2=0.01, p=0.934)

or age (t=-0.48, p=0.631) distribution of respondents who were not

included in the pairwise comparisons between clinical specialists

and pathology report extractions (n=814) compared to those

who were (n=1,152). Similarly, no differences were observed

for the comparisons between general practitioners and clinical

specialists by sex (χ2=0.34, p=0.561) or age (t=1.15, p=0.251).

For both pairwise comparisons respondents were more likely to

be included if they lived outside the south-east Queensland corner

(pathology reports and clinical specialists: χ2=9.63, p=0.022;

general practitioners and clinical specialists: χ2=27.07, p<0.001)

and if they lived in more socioeconomically disadvantaged areas

(pathology reports and clinical specialists: χ2=11.16, p=0.025;

general practitioners and clinical specialists: χ2=18.27, p=0.001).

However, neither remoteness (χ2=6.41, p=0.699) nor area of

socioeconomic disadvantage (χ2=5.90, p=0.921) was significantly

associated with the stage as reported by clinical specialists

(n=1417).

Reliability of stage reporting The level of agreement between the pathology reports and

clinical specialists was similar to the agreement between general

practitioners and clinical specialists (Table 1). Both comparisons

suggested about 82% of records within the pairwise comparisons

had identical stage, with weighted Kappa of nearly 0.80. There was

no evidence of any bias caused by the different (yet overlapping)

samples used for the pairwise comparisons, with levels of

agreement very similar when limiting the comparisons to records

with non-missing data for all three data sources.

The level of agreement varied by stage. Of those cancers

staged as ‘A’ by the clinical specialist, over 90% had the same

stage extracted from the pathology reports (K=0.73; Table 2).

The per cent agreement was slightly lower for cancers staged by

the clinician as B (79%) with nearly 20% of these cancers coded

Krnjacki et al. Article

2008 vol. 32 no. 4 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 381© 2008 The Authors. Journal Compilation © 2008 Public Health Association of Australia

instead as Stage A from the pathology reports. However, the kappa

estimate was similar (K=0.74) to that for Stage A. Agreement

with Stage C cancers was the highest of all stages (92%, K=0.82).

Agreement with Stage D cancers was lowest (27%; K=0.38), with

the majority (54%) of clinical Stage D cancers being coded instead

as Stage C from the pathology reports (Table 2).

In contrast, the level of agreement between clinician and GPs

was generally consistent across all stages (Table 2), with agreement

ranging from 75% to 85% (K= 0.68-0.77) for the four stages.

The level of agreement between GPs and clinical specialists

changed only slightly regardless of how the stage categories

were collapsed (Table 1). In contrast, the increased agreement

between pathology-reported stage and clinician stage for “A, B,

C/D” reflects the large proportion of clinician Stage D that were

coded as Stage C from pathology reports (Table 2). The even

higher agreement for “A/B, C/D” (Table 1) reflects the smaller

proportion of clinician Stage B that was coded as Stage A from

the pathology forms. The sensitivity and specificity estimates

(with specialist stage as the “true stage”) for this dichotomised

stage were 91.0% and 98.2% for pathology stage, and 88.3% and

90.5% for general practitioner stage.

Discussion This study found that the stage information extracted from

pathology reports had about 80% agreement with the stage

obtained from clinical specialists, and that this agreement

increased to 95% when collapsing stage to A/B and C/D. A

similar level of agreement between GPs and clinical specialists

was observed, however collapsing stage had little impact on the

levels of agreement.

When comparing the pathology-based stage with that of clinical

specialists, the most obvious difference was the under-reporting

of Stage D tumours when relying on pathology reports. This has

also been found for colorectal cancer stage in other Australian

states (New South Wales6 and Western Australia19). The lower

accuracy for more advanced cancers is due in large part to the

lack of information about metastases provided on the pathology

report.11 Only 14% of histology reports on colorectal cancer

tumours in the Western Australian Cancer Registry contained all

of the necessary information to be fully staged.19 Similarly, a study

conducted in New Zealand found that less than 4% of pathology

reports unequivocally reported the presence of metastasis.20

In contrast to the under-reporting advanced cancers of

pathology-based stage, the accuracy of GPs compared to clinical

stage were consistent across all four categories. Any disagreement

between GPs and specialist clinicians could reflect GPs having

access to less detailed clinical information and increased likelihood

of losing contact with the patient during the 12 months after

diagnosis.

Our study suggests that if four-level stage is required for research

purposes, then there would be a misclassification of stage of at least

20% using pathology records or GPs. The results for pathology

extractions are similar to those reported elsewhere for colorectal

cancer6 and other cancers.7-9,21 Using simulation analyses, Yu and

colleagues6 suggested that this imprecision could make previously

significant area-specific variation non-significant.

However, it is possible that a broader measure of stage could be

useful when used to adjust for disease spread in population-based

studies. The very high agreement between pathology extractions

and clinical specialists when the stage categories are collapsed

suggests a high degree of accuracy when using the collapsed

categories of ‘localised’, ‘locally advanced’ and ‘regional/distant’

and further into ‘localised/locally advanced’ and ‘regional/distant’.

This increase in agreement for the collapsed categories is not

simply due to fewer categories; the same process for GPs resulted

in very little change in the agreement.

Missing dataThere was insufficient information to extract stage from

approximately one-quarter (24.7%) of the pathology reports. This

proportion of missing data is considerably higher than the 14%

reported from the SEER registries22 and 18% in New South Wales.6

In this study, the pathology extracts were obtained by the research

officer as soon as possible after diagnosis, to facilitate prompt

recruitment for the main study. If additional relevant information

arrived in the cancer registry following recruitment of a patient,

then this subsequent information was not used in this study. A

subsequent review of 50 randomly selected cases that had missing

data in the main study noted that 18 (36%) of these were now able

to be staged. Assuming this proportion held across the remaining

missing records, it could reduce the per cent of missing pathology

stage to about 15%, within the range of other similar studies.

We did not include missing data in the reliability calculations.

This has particular relevance when stage information was available

from clinical specialists, but missing for the pathology reports

or general practitioners. Excluding these records may have over-

estimated the reliability estimates.

Limitations Estimates of agreement with clinical specialists for GPs and

pathology reports were based on pairwise comparisons using

different yet overlapping samples. Although this could potentially

bias the comparisons between the groups, when we repeated the

analysis using only those records with non-missing data from all

three sources very similar results were observed.

Only those people who agreed to take part in the initial study were

eligible to be staged. The relatively low response rate (57%), and

the under-representation of older (70 to 80 years) colorectal cancer

survivors, those with rectal cancer and those with more advanced

disease from the initial study12 may have implications for the

generalisability of these results. In particular the lower proportion

of patients with less advanced disease may have spuriously inflated

our reliability estimates. However, our findings were consistent with

those previously reported,11 in that stage information sourced from

pathology reports has least reliability when metastasis is involved,

and this limitation needs to be considered when sourcing stage

information from pathology reports.

Cancer Colorectal cancer stage information

382 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2008 vol. 32 no. 4© 2008 The Authors. Journal Compilation © 2008 Public Health Association of Australia

ConclusionsThe ability to accurately interpret inequalities in cancer survival

between population subgroups or changes over time requires

accurate information on cancer stage.1-3 Since clinical stage

information is not being collected in Australian population-based

cancer registries, the uncertainty of whether observed inequalities

in colorectal cancer survival23-25 are due to differentials in diagnosis

patterns, treatment practices, or a combination of both, limits our

capacity to intervene to reduce these inequalities for colorectal

cancer patients in this country.

This study, the first of its type in Queensland has demonstrated

that it is possible, and feasible, to reliably collect a broad measure

of disease spread for colorectal cancer patients from pathology

reports routinely submitted to the state cancer registry, and that

pathology reports are a better alternative than sourcing stage

information from the primary gatekeepers of medical care, general

practitioners.

Although this method of assessing disease spread cannot take

the place of clinical stage information, the limited progress

in developing population-based clinical cancer registries in

Australia means that, at least for the immediate future, sourcing

stage information for colorectal cancer patients from pathology

reports may be the best alternative. The results from this study

demonstrate that pathology-sourced stage is a valid measure of

disease spread when compared against stage information obtained

from clinical specialists.

ImplicationsThis method of collecting stage requires a lower level of

resources than other potential methods of collecting cancer

stage such as chart reviews, making it feasible to gather this

information for large-scale population-based studies on colorectal

cancer, and increase our ability to correctly interpret reasons for

observed inequalities in colorectal cancer survival. However,

that there are still differences between pathology stage and

clinical stage, particularly when metastasis is involved, highlights

the importance of integrating clinical stage information into

Australia’s population-based cancer registries to improve cancer

control in this country.

AcknowledgementsFunding for this study was provided by The Cancer Council

Queensland. The authors acknowledge Mrs Lyn McPherson and

Mrs Heather Day for their contribution to the data collection.

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