Determining Multiple Primaries

By now we have covered most of the general information in Section A in preparation for determining how many primaries to abstract. Review these guidelines as they are printed in the 2007 MPH General Instructions.

Section B is the step-by-step instructions to tell the registrar

  • When to use the rules (to decide how many primary malignancies are to be abstracted)
  • Which set of rules to use
  • Which module to use
  • Which rule to use

As previously noted, there are eight sets of site-specific rules and one set of rules for all "Other Sites". Remember that the benign and borderline central nervous system tumors and the hematopoietic primaries (lymphoma, leukemia and the other blood diseases) are excluded from the 2007 rules. Some sites also exclude Kaposi sarcoma.

The first step in using the 2007 MPH rules is to determine what the primary site is for your case. Read the General Instructions as a starting point. Usually the primary site is pretty obvious, like breast, colon, or kidney. Sometimes, however, you may be able only to get to the body system (for example, head and neck or urinary tract) and will have to use the site-specific multiple primaries rules to determine the exact primary site.

There will be occasions when there is no tumor present at the primary site, when the only cancer identified is a metastasis. In such situations, the physician may name the primary site in the medical record, and you can use that documentation to go to the appropriate set of rules. If there is no primary site named in the medical record, the case should be coded as "Unknown Primary Site" (C80.9) and the appropriate set of rules would be for "Other Sites".

Once you have determined the exact or approximate primary site, turn to the site-specific rules for that organ or body system and read the site-specific Equivalent Terms and Definitions.

Specific Rules

There are site-specific rules for the following primary sites:

  • Brain, malignant (C70.0 - C72.9; C75.1 - C75.3)
    Meninges, brain, spinal cord, cranial nerves, other parts of central nervous system, pituitary gland, craniopharyngeal duct, and pineal gland
  • Breast (C50.0 - C50.9)
  • Colon (C18.0 - C18.9)
    Note: Rectosigmoid and rectum are included in the "Other Sites" rules.
  • Head and neck (C00.0 - C14.8; C30.0 - C32.9)
  • Lip, oral cavity, salivary gland, tonsil, oropharynx, nasopharynx, pyriform sinus, hypopharynx, other and ill-defined sites in lip, oral cavity and pharynx, nasal cavity, middle ear, accessory sinuses, and larynx
  • Kidney (C64.9)
  • Lung (C34.0 - C34.9)
  • Malignant melanoma of skin (C44.0 - C44.9, histology code range 8720 - 8780 only)
  • Renal pelvis, ureter, bladder and other urinary sites (C65.9, C66.9, C67.0 - C67.9, C68.0 - C68.9)
  • Renal pelvis, ureter, bladder, urethral, paraurethral gland, urinary system, NOS

All Other Sites

Use the rules for "Other Sites" for all solid tumors that occur in primary sites not included in the site-specific rules. Click here for the list of primary sites and ICD-O-3 topography codes covered by the "Other Sites" rules.

The "Other Sites" rules are similar to the site-specific rules in their structure, but they cover all the sites that don't have or don't need a large number of special rules. Prostate is the most common site included in the "Other Sites" rules, but needs only one primary site rule and one histology rule. Other sites and histologies that have special rules include:

  • Retinoblastoma
  • Kaposi sarcoma
  • Thyroid

In addition, the "Other Sites" rules address combination and mixed histology code issues for the remaining sites not included in their own set of rules.

Next, review the medical record to count the number of tumors/masses/neoplasms/lesions that are mentioned. This will help you will determine whether the patient has a single tumor or multiple tumors that will be abstracted as a single primary.

  • Don't count separate tumors that are described as metastatic. For example, if the patient has a sigmoid colon cancer with multiple metastatic tumors in the liver, count only the sigmoid colon cancer primary.
  • When there is one or more macroscopic tumors with separate (microscopic) foci of tumor, do not count the (microscopic) foci.
  • Most of the time, only one tumor will be mentioned. It is still considered one tumor even if it extends directly to an adjacent organ. Count only distinct, macroscopic, non-metastatic tumors.
  • Sometimes, especially when a tumor is described as multicentric or multifocal, you may not know how many tumors are present.

Multiple Primary Rules Modules

Within each set of site-specific and "Other Sites" rules, there are three separate modules to determine how many primaries will require individual abstracts.

  • Unknown if Single or Multiple Tumors
  • Single Tumor
  • Multiple Tumors


Each module is an independent, complete set of rules. The rules are numbered consecutively to avoid confusion, but each module stands on its own. In general, there is only one rule in the module "Unknown if Single of Multiple Tumors" and one rule for "Single Tumor". The rest of the rules sort out whether "Multiple Tumors" are counted as a single primary/abstract or multiple primaries/abstracts.

Unknown if Single or Multiple Tumors

Use the "Unknown if Single or Multiple Tumors" module:

  • When there is no information about how many tumors the patient had. For example, you may be coding a case based only on a pathology report and you have no idea whether that patient has single or multiple tumors.
  • When there isn't enough information in the source documents. For example, say that a patient came to your facility for an excisional biopsy of a tumor. There was a note on the chart saying the patient had had a needle biopsy elsewhere. You don't know whether the needle biopsy was from that same tumor that was excised or from a different tumor. You simply don't have enough information.
  • At the central registry level, when you may get a report from hospital A about a needle biopsy on the right lung and later a report from hospital B or just a report from a pathology laboratory showing an excisional biopsy from the right lung. Here again, you don't know whether this is the same tumor.
  • When the medical record or report indicates that there are multicentric or multifocal tumors but the number is unknown.

When you don't have enough information about the number of tumors, use the "Unknown if Single or Multiple Tumors" module. For all sets of rules except malignant brain, there is only one rule in this module. That rule, M1, tells you to handle the case as a single tumor and abstract the case as a single primary. The rule in the "Unknown if Single or Multiple Tumors" module should be used only as a last resort when all potential sources of information—including contacting the clinicians on the case—have been exhausted. This rule also avoids over-counting tumors that may actually be dispersed metastases.

Single Tumor

Obviously, you will use the "Single Tumor" module when you have a known single tumor. But you would also use it if you had a single tumor with separate, microscopic foci. (Remember that the General Instructions say to disregard separate microscopic foci.) For all sets of rules except breast, there is only one rule in this module. That rule, usually M2, says "A single tumor is always a single primary" and one abstract is to be prepared for the case.

Multiple Tumors

The remainder of the rules in the Multiple Primaries section—numbered from M3 or M4 to as high as M18, depending on the site—determine whether multiple tumors are to be treated as multiple primaries or as a single primary. Many of the rules within the "Multiple Tumors" module will seem familiar to experienced registrars. This module is where former rules appear, such as topography codes different at the second or third character are different primaries or histology codes that are different at the first, second, or third digit are different primaries. You can use the "Multiple Tumors" module:

  • When you have multicentric tumors with the numbers of tumors identified
  • When you have multiple tumors with separate foci
  • When you have separate, non-metastatic tumors in different organs

Priority of Multiple Primaries Rules

  • Once you are in the appropriate module, start reading with the first rule in that module.
  • Keep reading until you find a rule that applies to your case.
  • Use the first rule that applies and stop. Do not skip down through the rest of the rules to see if another rule might apply.

The theory behind prioritizing the multiple primaries rules is to deal with the most important or most common situations first. As the rules go farther down the list, they apply to fewer and fewer cases. For example, in colon, it is very important to know whether multiple tumors in different segments of the colon are related to a genetic condition called familial polyposis; thus the first rule in the "Multiple Tumors" module, M3, says that multiple tumors in a patient with a history of familial polyposis are treated as a single primary. Subsequent rules deal with separate tumors in different topography codes, timing of diagnoses, invasive tumor diagnosed after in situ tumor, and so forth, in descending priority. In the "Other Sites" set, the first rule, M3, addresses the most common primary site, prostate (Adenocarcinoma of the prostate is always a single primary) Subsequent rules cover other, less common primary sites and histologies (retinoblastoma, Kaposi sarcoma, thyroid and bilateral ovary tumors), paired organs, and so forth.

Within each set of multiple primaries rules, the very last rule, "Tumors that do not meet any of the above criteria are a single primary", is intended to cover any situation not handled in rules with higher priority. This final "catch-all" rule will be applied very infrequently. Here again, the default is to a single abstract to avoid over-counting cancers that may not be true independent primaries.

The first rule that applies to your case tells you how many abstracts to prepare. If there is a single primary, prepare one abstract. If there are multiple primaries, set up the first abstract on your computer. (There are separate rules outside the scope of the Multiple Primaries and Histology Coding Rules that tell you how to sequence the primaries.) Set the other primaries/abstracts aside for now, because the next step is assigning the histology code for the first abstract.