How Often Do the New Rules Apply?

• Usage varies by site
• Multiple Primaries: less than 10% of patients
  • 90% of cases are single primaries
• Histology: 15-25% of cases
  • 75-85% of cases are basic, nonspecific (NOS) terms

Not all primary sites have the same kinds of issues that led to developing site-specific rules, so the frequency with which the new rules apply will vary by site. Some primary sites, like the central nervous system, only infrequently develop multiple primaries; others, like the urinary sites, have a very high likelihood of developing multiple cancers concurrently (at the same time of diagnosis) or sequentially (months or years later). Some diagnoses, like that of a prostate or a head and neck tumor, may use a limited range of histology codes. Other diagnoses, like that of a breast or kidney tumor, may include multiple terms that could represent a complex diagnosis or simply descriptive adjectives.

Overall, however, multiple primaries occur in less than ten percent of patients, based on an analysis of historic data by the SEER Program. That means that more than 90 percent of cases that a registrar abstracts are single primaries, and there is only one rule for those cases: a single primary is a single abstract. For the remainder of the cases, the registrar will have to refer to the multiple primaries rules for the site being abstracted in order to determine whether the case is one of multiple tumors abstracted as separate primaries or multiple tumors abstracted as a single primary.

Once the number of primaries has been determined for the case, the registrar will have to consult the histology coding rules for between 15 and 25 percent of individual abstracts. SEER's research showed that more than three-quarters of cases are coded to basic histologies, such as adenocarcinoma, NOS; squamous cell carcinoma, NOS; or duct carcinoma, NOS. The remaining cases could be situations where there are combinations of descriptive and diagnostic terminology, a biopsy with one diagnosis and a resection with another diagnosis, complex or mixed tumors, or other histology issues. For these scenarios, the registrar should always consult the histology coding rules, even if the case presented as a single primary.

Now that you know what the changes are, you may also realize that the new rules take much of the uncertainty out of determining whether a case has multiple primaries and how to code the histology. And, in order to make the registrar s choices even more straightforward, the 2007 MPH rules have one more important change—they are provided in different formats so that registrars can grasp the concepts more quickly based on how they learn. This innovation in formatting is discussed in the next section.