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Q35 - "Seed and Soil": Why Tumours Favour Specific Secondary Organs

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Cell Junctions, Extracellular Matrix & Cell Death Natural Selection: Modes & Fitness

Different types of primary tumours give rise to secondary tumours at different rates, and in characteristic places. (The primary organ is where the primary tumour occurs, the secondary organ is where the secondary tumour develops). To understand why, healthy mice (Mus musculus) were injected with cells from skin cancers which spontaneously developed in different mice: Arrow thickness = relative proportion of mice exhibiting the symptom. (1) Cells from the primary tumour were injected into the heart. (2) Cells from the primary tumour were injected into the tail vein. (3) Cells from a secondary tumour were injected into the heart. In (1, 2 & 3) cancer cells were recovered from the lymph of 100% of the injected mice within hours. In (4), cells from primary tumours were injected into the heart, and cells recovered from homogenised brain or lung were serially passed through fresh mice.

Figure 1 for Q35: “Seed and Soil”: Why Tumours Favour Specific Secondary Organs

Using the information and data, determine which of the statements are true or which are false.

A. The pattern of secondary tumours can be accurately predicted simply by how close different organs are to the primary tumour.
B. Crossing the blood vessel wall, in the secondary organ, is the limiting step in the formation of secondary tumours from circulating cancer cells.
C. Cells of a new secondary tumour evolve over time to thrive in the secondary organ.
D. Cancer evolves as it spreads to seed new secondary tumours more efficiently.
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Question reproduced from IBO 2017, Theoretical Exam B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key & worked solutions