Field Name




Behavior Code (BehaviorCode)




Behavior Code ICD-O-3



Field Length:  1

Record the behavior of the tumor being reported.  The fifth digit of the morphology code is the behavior code. 

Instructions for Coding

  • Code 3 if any invasion is present, no matter how limited.
  • If the specimen is from a metastatic site, code the histology of the metastatic site and code 3 for behavior
  • Gastro-intestinal stromal tumors (GIST) and thyomas are frquently non-malignant. However, they must be abstracted and assigned a Behavior Code of 3 if they are noted to have multiple foci, metastasis, or positive lymph nodes.

Note: The ICD-O-3 behavior code for juvenile astrocytoma (9421/1) is coded as 3.  Refer to the section "Case Reporting Requirements."






(Reportable for intracranial and CNS sites only)




(Reportable for intracranial and CNS sites only)

Uncertain whether benign or malignant

Borderline malignancy

Low malignant potential

Uncertain malignant potential


In situ and/or carcinoma in situ

Adenocarcinoma in an adenomatous polyp with no invasion of stalk

Comedocarcinoma, noninfiltrating (C50._)


Synonymous with in situ

Behavior code ‘2’

Bowen disease (not reportable for C440-C449)

Clark level I for melanoma (limited to epithelium)

Confined to epithelium

Hutchinson melanotic freckle, NOS (C44_)

Intracystic, noninfiltrating (carcinoma)

Intraductal (carcinoma)

Intraepidermal, NOS (carcinoma)

Intraepithelial neoplasia, Grade III (e.g., AIN III, LIN III, SIN III, VAIN III, VIN III)

Intraepithelial, NOS (carcinoma)

Involvement up to, but not including the basement membrane

Lentigo maligna (C44._)

Lobular, noninfiltrating (C50._) (carcinoma)

Noninfiltrating (carcinoma)

Non-invasive (carcinoma)

No stromal invasion/involvement

Papillary, noninfiltrating, or intraductal (carcinoma)

Precancerous melanosis (C44._)

Stage 0 (except Paget’s disease (8540/3) of breast and colon or rectal tumors confined to the lamina propria)




Primary site Invasive


Focus of invasion

Coding Instructions


Code behavior prior to neoadjuvant therapy when given.

Intracranial and CNS Tumors

Intracranial and CNS tumors with behavior codes 0 (benign) and 1 (borderline malignancy) are reportable beginning with January 1, 2004 diagnoses.

Code the behavior from CT scan, Magnetic Resonance Imaging (MRI), or Positron Emission Tomography (PET) report when there is no tissue diagnosis (pathology or cytology report). Code the behavior listed on the

scan. Do not use the WHO grade to code behavior.

Metastatic or Non-primary Sites

Cases reported to SEER cannot have a metastatic (/6) behavior code. If the only pathologic specimen is from a metastatic site, code the appropriate histology code and the malignant behavior code (/3). The primary site

and its metastatic site(s) have the same histology.

Code the behavior as malignant (/3) when malignant metastasis is present. Metastasis could be regional, nodal, or distant.

Example: Adenocarcinoma in situ with lymph nodes positive for malignancy. Code the behavior as malignant (/3). When the invasive component cannot be found and there are positive lymph nodes,

assign behavior /3 based on the positive lymph nodes.

Exception: For in situ breast cancer; code as non-invasive (/2) in the presence of isolated tumor cells or if cells are artifactually displaced from a previous procedure

In Situ

Clinical evidence alone cannot identify the behavior as in situ; a behavior code of /2 (in situ) must be based on pathologic examination.

Exception: Intraductal papillary mucinous neoplasm with high grade dysplasia (8453/2) of the pancreas is reportable based on imaging alone; histologic confirmation is not required.

In Situ and Invasive

Code the behavior as malignant (/3) if any portion of the primary tumor is invasive no matter how limited, i.e., microinvasion.

Example: Pathology from mastectomy: Large mass composed of intraductal carcinoma with a single focus of invasion. Code the behavior as malignant (/3).

Re-code the behavior as malignant (/3) when metastases are attributed to a tumor originally thought to be in situ.

Example: Right colon biopsy reveals tubulovillous adenoma with microfocal carcinoma in situ; right hemicolectomy is negative for residual disease. Later core liver biopsy consistent with metastatic

adenocarcinoma of gastrointestinal origin. Oncologist states most likely colon primary. Change the behavior code for the colon primary from /2 to /3. There were no other colon primaries in this case.

ICD-O-3.2 Histology/Behavior Code Listing

Behavior is the fifth digit of the morphology code after the slash (/). The standard reference for coding behavior is the ICD-O-3.2. Pages 27 through 30 in ICD-O-3 discuss behavior. The following general rules

are found on pages 29-30 in ICD-O-3.

• Usually a histologic term carries a clear indication of the likely behavior of the tumor, whether malignant or benign, and this is reflected in the behavior code assigned to it in the ICD-O

• Although only a few histologic types of in situ neoplasms are actually listed in the ICD-O, the behavior code /2 could be attached to any histology code if an in situ form of the neoplasm is diagnosed

• If the pathologist disagrees with the ICD-O behavior assignment in a particular case, code the behavior according to the pathologist’s description of the behavior even if that histology/behavior

combination is not listed in the ICD-O

The pathologist has the final say on the behavior of the tumor. ICD-O-3 may have only one behavior code, in situ (/2) or malignant (/3), listed for a specific histology. If the pathology report describes the

histology as in situ and the ICD-O-3 histology code is listed only with a malignant behavior code (/3), assign the in situ behavior code (/2). If the pathology report describes histology as malignant and the

ICD-O-3 histology code is listed only with an in situ behavior code (/2), assign the malignant behavior code (/3). See the Morphology and Behavior Code Matrix discussion on page 29 in ICD-O-3.

Example: The pathology report says large cell carcinoma in situ. The ICD-O-3 lists large cell carcinoma only with a malignant behavior (8012/3). Code the histology and behavior as 8012/2 as specified by the pathologist.