Repeatedly Identified PALB2 Exon 2–3 Large Genomic Deletion in Breast Cancer: Case Report and Clinical Implications

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Abstract PALB2 is a tumor suppressor gene essential for homologous recombination DNA repair. Pathogenic variants, including large genomic rearrangements (LGRs), predispose to hereditary breast cancer but remain underrecognized. We describe a 34-year-old woman with triple-negative breast cancer carrying a heterozygous PALB2 exon 2–3 deletion (Chr16:23649071–23649550), confirmed by multiplex ligation-dependent probe amplification (MLPA). She demonstrated a complete pathological response in the breast (ypT0N1a) after platinum-based neoadjuvant chemotherapy. A second unrelated patient in our cohort with hormone receptor–positive breast cancer harbored the identical deletion by bioinformatics analysis, with confirmatory MLPA pending. This repeatedly identified exon 2–3 deletion overlaps a ClinVar-reported pathogenic variant and supports the role of LGRs as clinically relevant PALB2 alterations. The observed platinum sensitivity underscores therapeutic opportunities, while the recurrence in an Indian cohort highlights the importance of incorporating LGR detection into routine hereditary cancer testing and cascade counseling.

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