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The Trp53 gene encodes several isoforms of elusive biological significance. Here, we show that mice lacking the Trp53 alternatively spliced (AS) exon, thereby expressing the canonical p53 protein but not isoforms with the AS C-terminus, have unexpectedly lost a male-specific protection against Myc-induced B-cell lymphomas. Lymphomagenesis was delayed in Trp53+/+Eμ-Myc males compared to Trp53ΔAS/ΔAS Eμ-Myc males, but also compared to Trp53+/+Eμ-Myc and Trp53ΔAS/ΔAS Eμ-Myc females. Pre-tumoral splenic cells from Trp53+/+Eμ-Myc males exhibited a higher expression of Ackr4, encoding an atypical chemokine receptor with tumor suppressive effects. We identified Ackr4 as a p53 target gene whose p53-mediated transactivation is inhibited by estrogens, and as a male-specific factor of good prognosis relevant for murine Eμ-Myc-induced and human Burkitt lymphomas. Furthermore, the knockout of ACKR4 increased the chemokine-guided migration of Burkitt lymphoma cells. These data demonstrate the functional relevance of alternatively spliced p53 isoforms and reveal sex disparities in Myc-driven lymphomagenesis.