[Menydh]

He explains it in an interview here (in Spanish):

Antonio Brú: "Bastaría potenciar el sistema inmune para superar el cáncer"

A translation of a part of the interview:

... what we discovered in vitro is that the dynamics of growth is equal in all tumours. I.e., there exists a dominant mechanism which is the same for all the types of cell lines. Such dynamics has three characteristics, which from the mathematical point of view are in a certain way equivalent:

1. The majority of cell activity in the tumours concentrates in the external part of them.
2. That it takes place what we call superficial difusion on the edge of the tumour. That is to say that the new cells which originate in the division of one of the cells of the edge of the tumour, move through it until they find a concavous position in which they find themselves surrounded by a bigger number of cells than they were in the position where they were generated.
3. That the growth of a cancerigenous colony is constant in time, except in the first phase (when there are few cells) in which the growth is logically exponential.

That the proliferation was restricted to the edge of the colony of tumour cells also meant that the cells of the inside of the colony do not proliferate at the same rythm as the cells of the outside. Which means that there exists a mechanism of cell inhibition of the cancerigenous cells. It is something similar to what is known in the normal (non tumourous) cells, as inhibition through contact (later we observed that in the practice it could be the same mechanism).

The next step was to confirm that this type of mechanisms also govern the growth of the tumour in vivo. We performed a large number of researches over fifteen different types of tumours, of which we obtained different histological section which allowed us to confirm that the most part of this proliferation was nearly always restricted to the edge of the tumour. We also verified in vivo the fundamental characteristics of in vitro growth; ie., that the mechanism was the same that we had observed in vitro. Besides, te morphological parameters that we measured in the colonies reproduced also during the in vivo growth phase. Therefore, in one way or another, we had discovered that there is a dynamic universality in all type of cell proliferation... and also in the tumour proliferation.

Then he goes on to explain:

According to this method of proliferation and growth, tumours must destroy first the tissue of the host in order to be able to invade it and occupy the new free space. The extracell matrix is degraded by the corrosiveness of the acidic environment created by the metabolism of the cells and by other substances released by tumour itself --among which are the metalloproteinases-- because the tumour need to continue degrading the tissue of the host in order to keep growing. No Physical scientist would be surprised from hearing that a mass that grows in the universe, what it needs above anything else is space. This is in contrast with the common belief that tumours invade first the tissue and then they destroy it. We have shown that it is right the opposite way.

And so on and so forth.. Ma'am.