Q26 — Intratumor Heterogeneity and Clonal Evolution Under Treatment

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license

Intratumor heterogeneity refers to distinct tumor cell populations within the same patient’s tumor. During tumor evolution, random mutations in genes (A-J) of different tumor cells result in distinct populations of cells (R1-R4) with different genetic and phenotypic profiles.

Panel A: a hypothetical tumor sample divided into four colored regions R1-R4. Panel B: an evolutionary tree showing mutations A-J branching into the four regions, with A on the trunk. Panel C: a copy-number plot along a chromosome showing a dip at gene E and a spike at gene F. Figure 1. A. A hypothetical tumor sample. B. The evolutionary relationship between the tumor regions of the sample, shown in A. Labels A-J refer to random mutations in genes of different tumor cells. C. The copy number alterations of genes E and F (the number of times a gene is present in the genome) along the chromosome (X: position along the chromosome, Y: copy number) from the tumor sample, shown in A. Note that the genetic defects related to genes E and F are known to be due to copy number alterations.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Intratumor heterogeneity frequently results in treatment failure and drug resistance.

B. Mutation in gene D is a better therapeutic target than mutation in gene A.

C. After treatment with the drug targeting mutation in gene C, Region R1 is more likely to expand than R4.

D. Based on Figure 1C gene E is a potential oncogene, while gene F is a potential tumor suppressor gene.

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Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF