Reporting of Cancer Stage at Diagnosis
Key findings
For diagnosis years 2013 to 2017, the stage distribution of breast, colorectal, lung and prostate cancers remained relatively constant. For breast and prostate cancers, the vast majority of cases were diagnosed as stage 1 or stage 2. For colorectal cancer, approximately half of all cases were stage 1 and stage 2. In contrast, almost half of all lung cancer was diagnosed at stage 4.
Why is this important to Ontarians?
- Clinical stage at diagnosis helps physicians to plan appropriate treatment and determine the likely outcome or course of the disease.[1] [2]
- From a system performance perspective, population-level stage at diagnosis facilitates cancer surveillance and healthcare planning. Knowing the distribution of cancer stage helps cancer agencies better evaluate the effectiveness of screening programs and prioritize resources for those cancers that have a higher incidence of advanced disease.[3]
- Staging describes the severity of a person’s cancer based on the size and extent of the original (primary) tumour and how far it has spread in the body.
- Stage at diagnosis can be described as stage 0 (in situ), stage 1 and 2 (localized), stage 3 (regional) or stage 4 (distant spread or metastasized). To date, the provincial cancer registry has not collected staging data on in situ cases.
- An unknown stage is the result of limited stage workup, limited documentation within the patient record, or both.
See Reporting of Cancer Stage at Diagnosis Methodology for technical information.
Results
- Breast, colorectal and prostate cancers had fairly consistent stage distribution from 2013 to 2017.
- Approximately 82% of breast, 74% of prostate and 50% of colorectal cancers were diagnosed at stage 1 and stage 2. All 3 of these cancers can be detected early through screening.
- While lung cancer did see an overall increase in stage 1 cases and a corresponding decrease in stage 4 cases, the volume of stage 4 cases of lung cancer, at 48%, continued to far surpass that for breast (5%), prostate (12%) and colorectal (18%).
- In colorectal cancer, 30% of cases were diagnosed as stage 3, which indicates regional lymph node involvement.
- “Unknown stage” means that an attempt was made to stage the case but the patient record was missing the necessary information. This could be because of a limited stage work-up in the clinical setting. “Not staged” means there was no access to the patient record (e.g., prostate cases seen only in a physician office). Fortunately, unknown stage rates have remained low over the reporting period at 0.36% for prostate, 0.57% for lung, 0.60% for breast and 2.5% for colorectal. The colorectal rate can be attributed in part to unknown depth of invasion.
- In terms of stage completeness, the stage capture rates for the period under review were 93.5% for breast, 90.5% for colorectal, 88.2% for lung and 91% for prostate.
Comparisons
Getting comparable data and measures from other jurisdictions is a challenge. Be aware of the different data definitions, methodologies and years used in indicators measured outside of Ontario. Jurisdictional comparison is still useful to provide a rough indication of how well Ontario is doing relative to other provinces and countries.
A number of jurisdictions publish comparable cancer staging data, including Norway, Scotland and England.
Breast cancer
Distributions of breast cancer stage at diagnosis are similar between Ontario, Norway and Scotland. Patients tend to be diagnosed during earlier stages of the disease. Across the jurisdictions, more than two-thirds of patients are diagnosed in the first 2 stages of breast cancer. In particular, more Ontarians appear to be diagnosed in stage 1 compared with Norway and Scotland. A summary of breast cancer incidence by stage of diagnosis is shown in Table 1.
| Stage | Ontario (2017) |
Norway* (2013-2017) | Scotland (2017) |
|---|---|---|---|
| 1 | 43.8% | 41.5% | 40.9% |
| 2 | 38.6% | 35.0% | 44.4% |
| 3 | 12.0% | 11.6% | 8.3% |
| 4 | 5.2% | 3.4% | 5.3% |
| Unknown | 0.5% | 8.3% | 1.2% |
* The Norwegian report indicated the percentage of patients by stage at diagnosis separately for males and females. For the purpose of this comparison, male and female cases have been combined.
Colorectal cancer
Early stage colorectal cancer is most comparable between Ontario, Norway and Scotland. Table 2 shows the stage distributions. The proportion of cases found in stage I is higher in Ontario compared with both Norway and Scotland. In addition, a comparison between Ontario and Scotland suggests that over 50% of colorectal cancer patients in Ontario are diagnosed in the first 2 stages compared with about 40% in Scotland.
| Stage | Stage (Norway) | Ontario (2017) |
Norway* (2013-2017) | Scotland (2017) |
|---|---|---|---|---|
| Stage 1 | Localized | 25.6% | 20.4% | 15.9% |
| Stage 2 | Regional | 25.5% | 50.1% (Regional combined) | 24.9% |
| Stage 3 | Regional | 29.5% | See above | 24.9% |
| Stage 4 | Distant | 16.2% | 20.9% | 24.0% |
| Unknown | Unknown | 2.2% | 8.6% | 10.4% |
* The Norwegian report indicated the percentage of patients by stage at diagnosis separately for males and females. For the purpose of this comparison, male and female cases have been combined. In addition, the Norwegian colon and rectal cases have been combined as colorectal cancer for this comparison.
Lung cancer
As shown in Table 3, the proportion of lung cancer cases found in stage 1 is higher in Ontario (24.2%) compared with both Norway (18.0%) and Scotland (17.4%). Across all 3 jurisdictions, however, most lung cancer patients were diagnosed at the last stage of the disease (stage 4 or distant).
| Stage | Stage (Norway) | Ontario (2017) |
Norway* (2013-2017) | Scotland (2017) |
|---|---|---|---|---|
| Stage 1 | Localized | 24.2% | 18.0% | 17.4% |
| Stage 2 | Regional | 8.3% | 27.4% (Regional combined) | 8.0% |
| Stage 3 | Regional | 20.7% | See above | 21.6% |
| Stage 4 | Distant | 46.6% | 39.0% | 46.1% |
| Unknown | Unknown | 0.3% | 14.7% | 6.9% |
* The Norwegian report indicated the percentage of patients by stage at diagnosis separately for males and females. For the purpose of this comparison, male and female cases have been combined. Data in Norway also include trachea (% of total cases).
** Includes a subset of stage 3 cases of lung cancer in Norway.
Prostate cancer
A large majority (75.0%) of Ontarians are diagnosed with prostate cancer during the first and second stages, compared with half of the cases in England, as shown in Table 4. However, more patients are diagnosed at stage 1 in England (30.0%) than in Ontario (23.8%). The overall pattern of incidence distribution is similar across both jurisdictions. As in breast cancer, more patients are diagnosed in the initial stages of prostate cancer than at later stages.
| Stage | Ontario (2017) |
England (2014) |
|---|---|---|
| 1 | 23.8% | 30.0% |
| 2 | 51.2% | 20.0% |
| 3 | 12.8% | 19.0% |
| 4 | 12.0% | 18.0% |
| Unknown | 0.2% | 13.0% |
About the sources of comparison
The Cancer Registry of Norway and its annual publication, Cancer in Norway 2017, summarizes the national cancer statistics. The period of diagnosis in Norway used for comparison is 2013 to 2017. The staging data from Scotland is published in Detect Cancer Early Staging Data 2018. The period of diagnosis in Scotland is 2010 to 2017. Cancer Research UK provides additional staging statistics. For the purpose of this comparison, we referred to its prostate staging data in England from 2014 (visit Prostate cancer incidence statistics).
Notes on staging classification
Norway: The stage group classification in Norway for colon and rectal (presented together as colorectal here) and lung are different from Ontario. For these disease sites, Norway uses the Dukes staging system, while Ontario uses the TNM staging system. The interpretation of Norwegian stage group maps approximately to Ontario’s as follows:
| Norwegian stage groups | Ontario stage groups |
|---|---|
| Localized | Stage 1 |
| Regional | Stages 2 and 3 |
| Distant | Stage 4 |
| Unknown | Unknown |
Note that while the majority of stage 3 lung cancer cases in Ontario would map to regional stage in Norway, a subset would fall under distant stage.
Scotland, England: The stage group classifications in Scotland and England are methodologically comparable to Ontario’s TNM staging system.
For more information
For more information on comparison between the Dukes and TNM staging systems, download the Colon and Rectum Cancer Staging information sheet from the American Joint Committee on Cancer. For more information on Dukes staging, visit Dukes’ staging system for the Cancer Research UK’s explanations.
For more information on stage capture, please visit Cancer Care Ontario’s website.