## SEER*Stat Prevalence Exercise 2b: Changing the Multiple Primary Selection

### Problem Statement

Repeat the analysis in Exercise 2a with one conceptual change: include the first tumor matching the selection criteria in each time interval. In Exercise 2a, a woman counted once in the total period and in only one interval. In this exercise, a woman will only count once in the total but could count once in multiple intervals.

### Key Points and Reminders

This exercise requires a different setting for the Multiple Primary Selection. This is the first time that we would like to use more than one primary cancer for an individual in the analysis. The only available option for including more than one primary cancer is "All Tumors Matching Selection Criteria." The individual statistics calculated in a prevalence session are only based on one tumor per person. For example, in this exercise, the statistics for each interval are based on one tumor per person. But, multiple tumors may be used in separate intervals.

Another application of the "All Tumors Matching Selection Criteria" option would be an analysis by cancer site where you would like to include the first primary for each cancer site. The All sites combined estimates would only include one tumor per person (the first primary of any type). But, a person may count toward more than one individual cancer site, for example, in both the lung and breast cancer estimates.

### Step 1: Open Exercise 2a's Matrix and Retrieve the Session

SEER*Stat matrix files include the session information used to generate the table. This information serves as documentation for the results and provides a convenient method for generating similar statistics.

• Open your saved matrix file from exercise 2a. If you did not save the file, use the file key.prev2a.spm.
• Open the Matrix menu and choose Retrieve Session.
• Two windows should now be open in SEER*Stat. Close the Matrix window and begin working in the Limited-Duration Prevalence Session window.

### Step 2: Selection Tab

On the Selection tab:

• In order to include multiple tumors for the 5-year interval (one per interval), change the Multiple Primary Selection option to "All Tumors Matching Selection Criteria."

### Step 3: Statistic Tab

• Now that "All Tumors Matching Selection Criteria" is selected on the Selection Tab, the sub-options under Discrete (Non-Overlapping) Intervals on the Statistic Tab are available. In order to include the first cancer per time interval, verify that First Cancer Per Interval (Intervals May Not Sum to Total) is selected.

No other changes to the original session are required.

### Step 4: Execute the Session

• Use the , or select Execute from the Session menu, to execute the session. As in the previous exercise, one or two warnings may be displayed, depending on your SEER*Stat preferences.
• The first warning is the same as the first warning you received in the previous exercise. It warns you that your session's Year variable might not be represented in the survival cohort table, and that the results may therefore be misleading. Click OK to continue.
• The second warning is similar to the the second warning from the previous exercise. It reminds you that only the first matching tumor for each individual will be counted towards any single prevalence estimate. Click OK to continue.
• A dialog will display the progress of the job. When the job completes, a new window will open containing the output table or matrix.

### Step 5: Check Your Results

Compare your results to the key for this exercise: key.prev2b.spm.

Then, compare the results to those from Exercise 2a (key.prev2a.spm). Note that the total time period and the earliest time period (>4-5) match.