Abstract P4-12-03: Patterns of progression in metastatic breast cancer: Does oligoprogression exist?
Authors: Bazan Jose G , Holbrook Amber , Jhawar Sachin , White Julia R 
Published: March 2020

Abstract
Background: While most patients with metastatic breast cancer (MBC) experience widespread disease progression on systemic therapy (ST), some have more limited progression, termed oligoprogression (OP). Patients with OP may benefit from local ablative therapies, such as stereotactic body radiation therapy (SBRT)/stereotactic radiosurgery (SRS), in order to avoid changing to the next line of ST. Here, we aim to evaluate patterns of progression in patients with MBC by breast cancer subtype (hormone-receptor positive/HER2- [HR+/HER2-], HER2+, and tripe-negative [TN]) to determine if and how often OP occurs. We hypothesize that OP does occur, and that it is more likely to occur in the HR+/HER2- and HER2+ BC subtypes compared to the TN subtype. Materials/Methods: We identified patients seen at our breast center from 1/2013-12/2017 with an associated ICD9/ICD10 code for metastases. We excluded patients that: did not have MBC; did not receive at least part of their treatment course for MBC at our institution; did not have imaging available for review. For the remaining cases, we reviewed each point at which a change in management was made to determine if OP of diffuse progression (DP) occurred. We defined OP as progression of disease in 1-4 lesions, with the exception of brain metastases, in which up to 10 lesions were allowed (provided patients received SRS and not whole brain radiation therapy). Findings such as malignant effusions, ascites, leptomeningeal disease, and lymphangitic/peritoneal carcinomatosis were scored as DP, regardless of the stability of other lesions. In addition, we collected demographic, tumor and treatment information. We set to determine the overall rate of OP and to compare the rate of OP amongst the HR+/HER2-, HER2+, and TN subtypes using a chi-square test. We also set to compare the overall survival in patients with OP vs. DP using the Kaplan-Meier method. A p-value&lt;0.05 was considered significant. Results: The query yielded a set of 1931 patients, of which 1017 met all inclusion criteria. This included 647 HR+/HER2- (63.6%), 187 HER2+ (18.4%), and 183 TN (18.0%) patients. About 29% (N=292) presented with de novo metastatic disease. Amongst patients with a distant metastatic recurrence, the median time to development of metastases was 49 months (interquartile range [IQR], 26-104 months) from original diagnosis. The median age at diagnosis of metastatic disease was 57 years (IQR=47-64 years). Most presented with &gt;4 metastases (84%). The median lines of ST for all patients was 3 (IQR=1-4). The crude rate of OP was 30% (N=306) and was highest amongst the HER2+ subtype (46.5%, 87/187) followed by HR+/HER2- (27.5%, 178/647) and TN (22.4%, 41/183), p&lt;0.0001. Intracranial metastases were seen as the only site of disease in 68 patients (40 HER2+, 20 HR+/HER2-, 8 TN) and with OP extracranial disease in 5 additional patients (3 HR+/HER2-, 2 HER2+). OP disease in the breast/axilla occurred as an isolated event in 28 patients (9.4%) and as a component of extracranial OP in 4 patients. Excluding the 32 patients with disease in the breast/axilla, nearly 90% of patients could potentially receive SBRT/SRS to the OP disease sites. Median follow-up for all patients was 32 months (IQR, 18-55 months) and at last follow-up, 866 of the 1017 patients had experienced at least one progression event. The 3-yr OS rate was 72.1% vs. 37.3% for patients in OP vs. DP groups, respectively (p&lt;0.0001). Conclusion: In summary, we found that OP does occur in MBC patients. The rate of OP is approximately 2-fold higher in HER2+ patients compared to TN and HR+/HER2- patients, reflected by a higher rate of intracranial OP disease. Nonetheless, all groups experienced an OP rate&gt;20% and the majority have disease potentially amenable to SBRT/SRS. These data serve to inform and support the development of prospective clinical trials evaluating the role of SBRT/SRS for oligoprogressive MBC.
Citation Format: Jose G Bazan, Amber Holbrook, Sachin Jhawar, Julia R White. Patterns of progression in metastatic breast cancer: Does oligoprogression exist? [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-03.