Why Site-specific New Rules Are Necessary
As the Histology Project conference calls began, it was quickly determined that an updated set of general rules could not address site-specific issues for several reasons:
- For each site or group of sites, there are prevalent histologies, such as the predominantly squamous cell cancers of the head and neck sites. By using site-specific modules, it is possible to identify those histologies and provide specific coding instructions that make it easier for the registrar to assign a histology code.
- There are site-specific disease manifestations, such as the field effect in urinary tract cancers and familial adenomatous polyposis in colon cancer, that make it difficult for the registrar to determine the number of primary cancers and to code histology. Those disease manifestations could be addressed in site-specific modules.
- The mixed and combination histology codes have caused a lot of confusion. The site-specific rules could provide tables that show which codes are valid for a particular site and also specify the terms that must be present in the pathology report in order to use the combination or mixed code.
Based on a review of all the issues, the following primary sites were determined to require site-specific rules:
- Brain & Central Nervous System, Malignant
- Head & Neck
- Malignant melanoma of skin
- Renal pelvis, ureter, bladder & other urinary
In part, these primary sites were chosen using the quality control principles of addressing those sites that comprise the majority of the data base (quantity) and those sites with the greater number of coding errors (high risk).
If you look at the first group, breast, colon, and lung—along with prostate—comprise over 60% of most central registry and facility-based registry databases. If an improvement can be made in the multiple primary and histology coding for that percentage of the database, it is a significant improvement. So, why doesn't prostate have a site-specific set of rules? The answer is that none was needed—there is no problem with determining multiple primaries for prostate (one for a lifetime) or with coding the histology (98% are adenocarcinoma, NOS).
Now look at the second group. All of these sites have a "high risk for errors".
- Brain tumor histologies have often led people to code a new tumor (glioblastoma multiforme) when the tumor is actually a recurrence of a previous glial tumor.
- Head and neck sites are so close together that it is difficult to assess where the tumor originated. It is frequently unclear if there is a contiguous tumor or discontinuous.
- Melanoma has long been a problem with whether to use laterality to determine multiple primaries.
- The urinary sites (renal pelvis, ureter, and bladder) are known for problems with field effect that make it difficult to determine the number of primaries.
All of these issues could be addressed in the site-specific coding modules.
The Histology Committee determined that it was necessary to develop site-specific rules in order to
- Address problems identified with cancer site groups
- Address specific histology coding for specific cancer sites
- Address grouping of histologic terms
- Differentiate between umbrella (NOS) terms and specific histologic types and subtypes
- Address the issue of mixed and combination codes.
These issues were considered and dealt with during the development of the 2007 Multiple Primaries & Histology Coding Rules. The new rules incorporate updates to the previous rules by making them site/system-specific and listing the rules in priority order. Furthermore, the new rules are "one stop shopping"; in other words, all the rules are in one place—no more sticky notes in various manuals, looking through multiple documents to find the applicable rule and any errata or changes. In addition to making the rules more usable by registrars, they now are also adaptable to computer applications.
There are new rules to cover virtually every possibility in every site, but here are a few common sticky situations that are capably handled in the new rules.
- A papillary carcinoma in the right lobe of the thyroid and a follicular carcinoma in the left lobe within 60 days of diagnosis (one primary)
- Four separate papillary transitional cell carcinomas in the distal ureter and base of bladder (one primary)
- Inflammatory breast carcinoma in both breasts (one primary)
- Lobular carcinoma in the right breast and a mirror image lobular carcinoma in the left breast (two primaries)
- Multiple biopsies of invasive squamous cell carcinoma on the left tonsillar pillar with in situ spread onto the posterior wall of the oropharynx and base of tongue (one primary)
- Malignant polyps from the transverse colon to the sigmoid in a patient with familial polyposis (one primary)
- A malignant melanoma on the right scapula and a malignant melanoma on the left chest (two primaries)
The new rules take the kinks, exceptions, and most of the gray areas out of counting multiple primaries, and clarify the definitions of many morphology codes. In particular, the histology coding rules will clarify how to handle the relatively frequent cases where there is a mix of histologies or a mix of descriptive and diagnostic terminology in the path report.