AbstractAbstract 1618 Introduction:Primary breast lymphoma is a rare type of non-Hodgkin lymphoma (NHL), representing about 1% of breast tumors and 2% of extranodal NHL. Diffuse large B-cell lymphoma (DLBCL) is the most common primary subtype presenting in the breast. Due to the low incidence of primary breast DLBCL, outcome data is limited. The aim of this study was to retrospectively assess the natural history of primary breast DLBCL in the pre and post rituximab eras, with specific emphasis on the incidence of local, systemic and central nervous system (CNS) relapses. Methods:Data was retrospectively collected on patients with primary breast DLBCL from seven USA academic medical centers. Institutional review board approval was obtained at each participating site. Patients were identified through institutional databases and tumor registries at each site. Charts were reviewed to obtain demographic and clinical variables including treatment history and dates of relapse and death when applicable. Only patients with stage I/II disease (involvement of breast and localized lymph nodes) were included. All histologies apart from primary DLBCL were excluded. Overall survival (OS) was calculated from the diagnosis date to the date of death or last follow-up. Time to Progression (TTP) was calculated from diagnosis data until the date of pathological evidence of recurrence or death. Data were summarized using descriptive statistics, and survival was analyzed using the Kaplan-Meier method. Results:Between 1984 and 2012, 75 patients were identified who met the eligibility criteria. The median age was 62 years (range 17–87); 81% presented with a palpable mass; 12% had their disease detected incidentally by mammography; 4% presented with B-symptoms; 59% had right breast involvement; 67% had stage I and 33% had stage II disease. The stage-adjusted international prognostic index (IPI) score was 0 in 28% of patients, 1 in 41%, 2, in 25%, 3 in 4% and 4 in 1%. 91% of patients were treated with chemotherapy; 31% of these were treated in the pre-rituximab era and 69% received rituximab. Radiation therapy (RT) was utilized in 68% of patients and was the only treatment modality in 8% of those receiving RT. 8% of patients received CNS prophylaxis with intrathecal chemotherapy. After a median follow-up of 4.5 years (range 0.6 – 20.6 years), the Kaplan-Meier estimated median TTP was 10.4 years (95% CI 6.2 – 14.6 years) and the median OS was 14.6 years (95% CI 6.5 – 22.6 years). The 5-year TTP and 5-year OS were 65% (95% CI 53–77%) and 75% (95% CI 64–86%) respectively. Among the patients who relapsed, 67% occurred within the first 2 years. A total of 7 relapses in the breast were observed, none in patients treated with combination of chemotherapy and RT. In univariate analysis, rituximab exposure was not associated with any difference in TTP or OS. The stage-adjusted IPI was associated with OS; the 5-year OS was 88% (95% CI 79–98%) in patients with a score of 0–1 versus 48% (95% CI 25–71%) in those with a score of 2–4 (log rank p < 0.001). The very limited-disease group with a stage-adjusted IPI of 0 had a 5-year OS of 94% (95% CI 83–100%) compared to all others who had a 5-year OS of 67% (95% CI 52–81%; log rank p = 0.001). There was no difference in TTP and OS in patients with solitary versus multiple breast masses or between patients with tumors less than versus more than 7cm. Patients receiving RT in addition to chemotherapy had a longer TTP than those who did not (log rank p = 0.03), but RT was not associated with an improved OS. Patients who relapsed and underwent stem cell transplant (SCT) had similar OS to those who never relapsed. Ten patients (13%) had CNS relapse (3 with leptomeningeal disease, 5 with brain parenchymal disease and 2 with both). All CNS relapses occurred within the first 2.8 years from the time of diagnosis. There was no difference in the rate of CNS relapse in the patients who received IT prophylaxis versus those who did not. Conclusions:In this multicenter study, the largest published to date, primary breast DLBCL appears to have a worse prognosis than early-stage DLBCL in nodal or other extranodal sites. RT was associated with improved TTP. Patients who relapsed were successfully salvaged with SCT, and had similar survival times to those who never relapsed. A high CNS relapse rate (∼1 in 8 patients, including parenchymal disease in 70%) was observed. The small numbers preclude definitive conclusions on the value of intrathecal prophylaxis or the utility of rituximab. Disclosures:No relevant conflicts of interest to declare.

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