Patterns of treatment and their outcomes in primary breast lymphoma; a comprehensive population-based analysis.

BACKGROUND: Primary breast lymphoma (PBL) is managed differently among centers, using surgery, systemic therapy and/or radiation. With data derived from the National Cancer Database (NCDB), we aim to describe treatments utilized in the United States, estimate the overall survival (OS) of different therapeutic modalities and determine the role of systemic therapy in patients with PBL. METHODS: We conducted a retrospective cohort study using de-identified data from the NCDB. The NCDB provided records of 4616 patients diagnosed with PBL between 2004 and 2015. We excluded patients diagnosed with HIV, with no survival data, not treated in the reporting facility, without histologic confirmation, with stage III/ IV disease and for whom surgery, radiation, or systemic therapy was contraindicated. Both propensity score weighting and Cox models were used to obtain adjusted estimates. Based on histopathology, PBL was classified into indolent (I-PBL) and aggressive (A-PBL). RESULTS: In a sample size of 2063 PBL patients, the median age was 67 years (interquartile range (IQR): 57-78), and 97% were females. In 1027 patients with I-PBL, the median follow-up was 66 months (95% confidence interval (CI): 32.6-107.2) and 60% of patients had extranodal marginal zone subtype. Systemic therapy did not improve adjusted-OS (median: 154 vs. 143 months, P = 0.36) (Hazard ratio (HR): 0.86, 95% CI: 0.60-1.25, P = 0.42). The treatment arms associated with the highest adjusted 5-year OS were as follows: radiation (85%), surgery (79%), systemic & radiation (87%) and radiation & surgery (87%) (P = 0.9). In 1036 patients with A-PBL, the median follow-up was 67.4 months (95% CI: 35.9-105), and 87% of patients had diffuse large B-cell subtype. Patients with A-PBL who received systemic therapy had an improved adjusted-OS (median: 115 vs. 72 months, P < 0.01) (HR: 0.45, 95% CI: 0.38-0.53, P < 0.001). The treatment arms associated with the highest adjusted 5-year OS were: systemic (69%), systemic & radiation (77%), systemic & radiation & surgery (79%) and systemic & surgery (79%) (P = 0.4). CONCLUSIONS: Systemic therapy used as first-line treatment is essential in A-PBL. Local therapy in the I-PBL using surgery and/or radiation is effective in long-term disease control. There is significant variation in front-line treatment modalities utilized in PBL across the US, many associated with similar outcomes.