Abstract 889: Evaluating the case definition of inflammatory breast cancer

Abstract

Abstract Background: Inflammatory breast cancer (IBC) is recognized as an aggressive form of breast cancer requiring neoadjuvant chemotherapy. Although IBC affects only a small percentage of breast cancer patients, the estimated 4,810 new cases for 2009 exceeds the number of women diagnosed with other cancers, such as acute lymphocytic leukemia and chronic myelocytic leukemia (as reported by the American Cancer Society). Research on IBC is hampered by the absence of an agreed upon case definition. While the American Joint Committee on Cancer (AJCC) relies on clinical features (more than half of the breast being involved with redness, warmth and edema), the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program focuses on pathologic confirmation. This study was undertaken to determine whether the outcome of IBC differs among patients who meet IBC criteria by AJCC, SEER, and private practitioners to try to improve the case definition for research purposes. Methods: This is a retrospective study of 121 patients in The George Washington University Medical Center IBC Registry who were classified as an IBC case by AJCC, SEER or private practitioners. We grouped these IBC cases into four epidemiological categories: (1) clinical-pathologic presentation of disease involving more than half of the breast, (2) clinical-only presentation of disease involving more than half of the breast, (3) clinical-pathologic presentation of disease involving less than half of the breast, and (4) clinical-only presentation of disease involving less than half of the breast. Note that Categories 1 and 2 meet AJCC criteria, while Categories 1 and 3 meet SEER criteria for IBC. We used an unadjusted Cox proportional hazards model to test the homogeneity of the progression-free survival (PFS) curves among these four epidemiological categories. Results: Of the 121 IBC cases, 33.1% (n=40) were classified as Category 1, 16.5% (n=20) were Category 2, 25.6% (n=31) were Category 3, and 24.8% (n=30) were Category 4. Using Category 4 as the reference group, the Cox proportional hazards model yielded insignificant hazard ratios (95% CI) of 1.69 (0.82, 3.51), 0.80 (0.28, 2.28), and 1.98 (0.95, 4.12) for Categories 1, 2, and 3, respectively. Applying the Score test, we found no significant difference in the PFS curves among the four epidemiological categories (χ2=5.87, p=0.12). Conclusions: The case definitions of IBC as proposed by the AJCC and SEER are inadequate. This study suggests that IBC as identified by private practitioners not meeting these criteria have the same poor prognosis as those meeting the case definitions of these national organizations. Preliminary laboratory studies support the conclusion that women with clinical evidence of IBC not involving half of the breast and with no documentation of involvement of the dermal lymphatics have the same disease as those meeting AJCC and SEER diagnostic criteria. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 889.