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NAACCR Data Dictionary
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Multiple Primary Rules/Solid Tumor Rules

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SEER rules have been the de facto standard for determining the number of primary cancers in the U.S. for both central and hospital-based registries. The 2018 Solid Tumor Rules replace the 2007 Multiple Primary and Histology (MP/H) Rules for the following eight site groups: Head & Neck, Colon (includes rectosigmoid and rectum for cases diagnosed 01/01/2018 and forward), Lung, Breast, Kidney, Urinary Sites, Non-malignant CNS, and Malignant CNS and Peripheral Nerves.

The 2007 Multiple Primary & Histology Rules remain in effect for the other sites not listed above effective with cases diagnosed 01/01/2007 to 12/31/2020. The cutaneous melanoma site rules will be revised for 2021 implementation to incorporate the WHO Classification of Skin Tumours, 4th Edition and the Other site rules will be revised to include GYN, soft tissue, thyroid, and other site-specific solid tumors for 2022 implementation.

The Canadian Cancer Registry rules were the Canadian standard for the Canadian Cancer Registry database between 1992 and 2006. See the Canadian Cancer Registry Collection Documentation 5 for details. For cases diagnosed on or after January 1, 2007, the Canadian Cancer Registry adopted the SEER 2007 Multiple Primary and Histology Coding Rules.

Until all registries in Canada adopt the same set of rules to determine multiple primaries, the Canadian Cancer Registry publishes data nationally using the IARC multiple primary rules. The IARC rules have the effect of defining fewer cases than do any of the US multiple primary rules. A computer algorithm is available through IACR/IARC which identifies which U.S. cases would not be reportable under IACR/IARC multiple primary rules.

A rule requiring that an invasive tumor diagnosed more than two months after an in situ tumor of the same site be reported as a subsequent primary was reviewed by the Uniform Data Standards Committee and adopted on April 26, 1994, effective with tumors diagnosed in 1995 and later. This rule remains in effect and is incorporated into the 2018 Solid Tumor Rules as follows:

  • An invasive tumor following an in situ tumor more than 60 days after diagnosis is a multiple primary.
    • Note 1: The purpose of this rule is to ensure that the case is counted as an incident (invasive) case when incidence data are analyzed.
    • Note 2: Abstract as multiple primaries even if the medical record/physician states it is recurrence or progression of disease.

This important rule affects how the tumor will be counted in published statistics. Except for bladder, in situ tumors are not usually included in published incidence rates. Without the reporting of these invasive cancers per the rules above, rates of invasive breast cancer would be underreported. CoC, with its emphasis on clinical data, did not adopt this exception to the general rule until the 2007 MP/H rules were implemented.

In the Canadian Cancer Registry database 1992-2006, if there was an in-situ cancer followed by an invasive cancer at the same site and histology, only the invasive primary was retained, the date of diagnosis was linked to the invasive primary. The Canadian Cancer Registry multiple primary rules did not allow an in situ and invasive primary to be retained for the same site and histology.