Abstract P4-16-02: A survival benefit from locoregional radiotherapy for node-positive and CMF treated breast cancer is most significant in Luminal A tumors
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Abstract P4-16-02: A survival benefit from locoregional radiotherapy for node-positive and CMF treated breast cancer is most significant in Luminal A tumors
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<jats:title>Abstract</jats:title>
<jats:p>Background: Between 1978–1986, 318 premenopausal women treated with mastectomy for lymph node positive breast cancer, were randomized to CMF chemotherapy alone vs. CMF chemotherapy and adjuvant radiotherapy (RT) to the chest wall and regional lymph nodes. After 15 years of follow-up, post-mastectomy RT was associated with a statistically significant 29% relative risk reduction in mortality. Recent evidence suggests that Luminal A tumors, identified using hormone receptors and Ki67, have a particularly favorable prognosis. We retrospectively identified the Luminal A tumors from this clinical trial cohort to determine if the response to postmastectomy RT differed among Luminal A and non-Luminal A tumors.</jats:p>
<jats:p>Methods: 203 archival breast tumor samples from this study were used to construct a tissue microarray. Luminal A tumors were identified using an immunopanel consisting of: estrogen receptor, progestorone receptor, Her2, and Ki67. Luminal A tumors were defined as either ER or PR positive, Her2 negative, and Ki67 &lt; 14%. Kaplan-Meier estimates and the log-rank test were used to test the differences in locoregional relapse free survival (LRFS) and breast cancer specific survival (BCSS). Interaction between treatment and Luminal A/Non-luminal A were tested using Cox regression analysis.</jats:p>
<jats:p>Results: The intrinsic subtype was successfully determined in 144 breast tumors, and 49 were classified as Luminal A (34%). Survival outcomes at 10 years are summarized in Table 1:</jats:p>
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<jats:p>Conclusion: Our study examines the outcome of Luminal A tumors in patients with higher risk (premenopausal and lymph node positive) breast cancer treated with CMF chemotherapy. We observed that both subjects with Luminal A tumors and non-Luminal A tumors appear to demonstrate improved locoregional control with post-mastectomy RT, although this was only significant for Luminal A tumors. The non-significant interaction test suggests that there is no observable difference in radiosensitivity in this limited study population. However, the improvement in BCSS with post-mastectomy RT was only significant in the subjects with Luminal A tumors, and the interaction test was statistically significant.</jats:p>
<jats:p>Our results raise the possibility that patients with non-Luminal A breast tumors are at higher risk of occult metastatic disease at presentation, and may not derive a survival benefit with improved locoregional control in the setting of CMF chemotherapy. In contrast, locoregional control has a significant effect on survival with Luminal A tumors. Our study suggests that a favorable Luminal A diagnosis should not be a reason to omit regional radiotherapy in node positive patients, as it is this subgroup that may derive the greatest benefit.</jats:p>
<jats:p>Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-16-02.</jats:p>