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SEER Inquiry System - Report
Produced: 01/20/2026 5:35 PM
Question 20230018
Inquiry Details
References:
2023 SEER Manual, 203-208. Chemotherapy
Question:
SEER Manual/First Course Treatment--Chemotherapy: Does the First Course of Treatment end when subcategories change for treatments such as hormone therapy or immunotherapy or is that instruction specific to chemotherapy? See Discussion.
Discussion:
Treatment for estrogen receptor positive (ER+) breast cancer started with tamoxifen (non-steroidal estrogen subcategory) and switched to letrozole (non-steroidal aromatase inhibitor subcategory). Patient being treated with immunotherapy, Avastin (cytostatic agent-antiangiogenesis agent subcategory), and then changed to Atezolizumab (monoclonal antibody subcategory).
Is Atezolizumab a new course of therapy because it is a different subcategory?
Answer:
Answer updated April 2025
A change in the subcategory for a hormone drug does not indicate the end of First Course of Treatment because different hormone therapies generally achieve the same result. For example, some forms of breast cancer are estrogen-dependent and the various subcategories of hormone drugs used to treat them, such as gonadotropin-releasing factor agonists, aromatase inhibitors and estrogen antagonists, all achieve the same result - to block estradiol effects in these tumors.
Similarly, a change in immunotherapy is not a new course of treatment.
However, if a change to hormone therapy or immunotherapy is due to a change in the patient's ER, PR, or Her2 status, this could signify a new course of treatment.
The instruction in the SEER Manual is specific to chemotherapy. Chemotherapy is the only systemic treatment for which a change in the subcategory of a drug indicates the end of First Course of Treatment, due to the fact that different chemical agents damage cancer cells in different ways and at different phases in the cell cycle.
