Haemoncolyte
Haemoncolytes are a type of familiar created by members of the Adeptus Mechanicus.
They are vat-grown creations from a techpriest's own flesh and blood, typically designed to absorb any tumours or poisons generated by the techpriest, effectively cleansing their bodies and allowing them to live longer. The imperfections are passed on to the haemoncolyte through an umbilical connection.
Haemoncolytes rapidly age as they become covered in liver spots and lumpen growths taken from their techpriest counterpart.