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Medical Auditing & Coding Blog


Coding for Primary Cancer and Metastatic Cancers

When coding malignant neoplasms, there are several coding guidelines we must follow: 
To properly code a malignant neoplasm, the coder must first determine from the documentation if the neoplasm is a primary malignancy or a metastatic (secondary) malignancy stemming from a primary cancer.

Accurate sequencing for primary and secondary cancer depends on which site is being treated or focused upon at the current encounter.  For instance, a patient who has primary breast cancer (C50.xx) who is now seen for metastatic bone cancer will have a code for the secondary bone cancer (C79.51) sequenced before a code for the primary breast cancer (C50.xx).

When a current cancer is no longer receiving treatment of any kind, it is coded as a history code. For instance, the patient had breast cancer (C50.xx) and underwent a mastectomy, followed by chemoradiation.  The provider documents that the patient has no evidence of disease (NED).  The breast cancer is no longer being treated and you would use a history code (Z85.3).  But let's say she is now put on an oral estrogen receptor (e.g., Tamoxifen); the documentation will determine if the breast cancer should be coded as current or as a history code…if the provider notes Tamoxifen is being given as treatment, the breast cancer would be considered current (C50.xx) as it would still be under active treatment.  If the documentation states the Tamoxifen is given as a prophylactic measure, then the cancer would be coded as a history (Z85.3) because a prophylaxis is not considered active treatment. 

If the site of the primary cancer is not documented, the coder will assign a code for the metastasis first, followed by C80.1 malignant (primary) neoplasm, unspecified.  For example, if the patient was being treated for metastatic bone cancer, but the primary malignancy site is not documented, assign C79.51, C80.1.  If the documentation states the cancer is a metastatic cancer, but does not state the site of the metastasis, the coder will assign a code for the primary cancer, followed by code C79.9 secondary malignant neoplasm of unspecified site.  An example is if the patient is being treated for breast cancer that has metastasized but the provider does not state to which site the metastasis has occurred, assign C50.xx, C79.9.

If the patient encounter is for the purpose of receiving chemotherapy (Z51.11) or immunotherapy (Z51.12) or radiation therapy (Z51.0), in the outpatient setting, the therapy encounter code is always the first listed code, followed by a code for the cancer that is being treated.  If more than one therapy is being provided at the same encounter, then the therapy codes are assigned as the first and second codes (and third if all 3 therapies are provided) in any order, followed by a code for the cancer that is being treated. 

Always follow ICD-10-CM Official Coding Guidelines and refer to any AHA Coding Clinics for guidance on coding for malignancies.  

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