Macrostomum lignano is characterized by its elevated regenerative ability conferred by its high percentage of stem cells (the highest recorded for any animal). M. lignano is already used as a model organism for addressing fundamental questions of stem cell biology, aging, regeneration, and reproduction, but not yet cancer.
M. lignano larvae were isolated into separate wells of 24-well plates. After reaching maturity (30 days), the experimental plates were exposed to 5 Gys of X-rays every 4 days for a total of a 25 Gy exposure. We observed phenotypes that may be attributed to the acute effect of irradiation (e.g. blisters) but we recorded two types of phenotypes that may be a result of long-term effects of exposure to radiation. We observed enlarged testis and dark regions/masses that appeared statistically significantly more frequently in the treated animals (Fisher exact test, p=0.0026). Preliminary histological analyses of the enlarged testis suggest a benign testis enlargement due to an aberrant growth of the testes and an accumulation of aberrant spermatozoa. Importantly, we found that, similar to cancer, the dark masses can grow in size over time and the histological analysis confirms that the observed masses are composed of cells completely different from surrounding normal cells. Notably, we observed that those masses can develop and then completely disappear through an observed method of ejection. M. lignano offer the unique possibility to study in vivo cancer development in a simple organism that can easily be cultured in the lab in large numbers.