The topic of tumour self-seeding, i.e. the idea that tumour cells leaving the primary via the blood stream come back and boost its growth has been widely debated and investigated (here, here and here to mention a few). I have recently, together with collaborators from Moffitt Cancer Center in Tampa, developed and analysed a model of this phenomenon. Our findings were published the other day in Royal Society Interface although a preprint has been on the arxiv for a while. To summarise: the phenomenon of tumour self-seeding is highly unlikely to contribute to the growth of the primary unless the circulating tumour cells form micrometastases which allow for an expansion in cell number sufficient to balance the severe losses that this hematic round trip incurs.