Divergent clonal selection dominates medulloblastoma at recurrence.

Area of Science:

• Oncology
• Genomics
• Cancer Biology

Background:

• Targeted anti-cancer therapies aim to improve survival and reduce toxicity by targeting specific genetic alterations in cancer.
• Understanding the genetic landscape of recurrent tumors is crucial for developing effective treatment strategies.

Purpose of the Study:

• To investigate the genetic basis of tumor recurrence after therapy in medulloblastoma.
• To determine if genetic divergence occurs between primary and recurrent tumors in response to treatment.
• To identify the clonal origins of recurrent medulloblastoma and explain the failure of targeted therapies.

Main Methods:

• Utilized a transposon-driven, functional genomic mouse model of medulloblastoma treated with 'humanized' in vivo therapy.
• Performed whole-genome sequencing on 33 pairs of human diagnostic and post-therapy medulloblastomas.
• Analyzed genetic events in murine and human medulloblastoma samples at diagnosis and recurrence.

Main Results:

• Recurrent murine medulloblastoma showed minimal overlap (<5%) with genetic events from matched diagnostic samples.
• Human medulloblastomas exhibited significant genetic divergence after therapy, with <12% of diagnostic events retained at recurrence.
• The dominant clone at recurrence in both species originated from a pre-existing minor clone present at the time of diagnosis.

Conclusions:

• Tumor recurrence is driven by clonal selection of pre-existing minor clones, leading to substantial genetic divergence from the primary tumor.
• The absence of therapeutic targets in the recurrent tumor clone explains the clinical failure of targeted therapies.
• These findings provide a direct explanation for the ineffectiveness of targeted therapies in prior clinical trials.