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Tumor Tip of the Week – SEER Appendix C Coding Guidelines Breast

Scenario:  2021 Mastectomy found to have DCIS in RUOQ & RLOQ, Invasive ductal carcinoma in RUOQ


Question: How would you code primary site?

  • C504 UOQ
  • C509 Breast NOS

Answer: C504 UOQ



  1. Breast Solid Tumor Rules Table 1: Primary Site Codes
    • Refer to the SEER Manual and COC Manual for a priority list for using documents such as mammograms, operative reports, and pathology reports to determine the tumor location.
  2. SEER Program Coding and Staging Manual 2021 Appendix C Coding Guidelines Breast
    • Code the subsite with the invasive tumor when the pathology report identifies invasive tumor in one subsite and in situ tumor in a different subsite or subsites.
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