Comparative Neuro-oncology: From Man to Insect

Abstract

Nervous-system tumours are read here not as a tax on neural sophistication but as failure modes of a single developmental switch — the gate between self-renewal and terminal fate, enforced by the retinoblastoma protein and its pathway. Descending a gradient of neural organisation rather than a cladogram, from the human eye through mouse, large mammals, fish, amphibians and the invertebrate floor to the Drosophila larval brain and below, the essay argues that the same lesion recurs at every rung: a proliferating neural progenitor that fails to leave the cycle. Two modes of failure are distinguished — arrest, a progenitor caught before its fate, and reversion, a differentiated cell driven back to a stem-like state — and shown to be one switch opened from opposite sides, with the descent travelling increasingly by reversion as it enters the great regenerators. Along the way it reframes Peto's paradox as a statement about the finished soma rather than the developing organ, insists on reading the comparative record against ascertainment bias and the anthropogenic distortion of breeding, pollution and therapy, and locates the cell of origin drifting with each animal's architecture from cone precursor to ciliary epithelium to Schwann cell to neuroblast. The neural tumour proves conditional on a concentrated nervous system built from dividing cells: it makes its final appearance in the insect brain and vanishes below the bilaterians, where cancer withdraws to the germline and the blood, even as malignancy itself is shown to be as old as animal multicellularity.