Large bleeding lump on female dogs vagina

This lump came up overnight it seems, she has been licking it at times, eating and drinking does not appear unwell. This lump drops blood, will it go on its own or will it need to be surgically removed?

Hello!  My first concern for this lump is not necessarily the type of cell involved, but that the lump itself appears to be in a position to be rubbed, to scrape against things, to bleed and to become infected, not to mention being potentially very painful in that position.  Licking is a sign of pain and irritation and also further damages / spreads around the cells being licked.  The cells involved may be delicate lining cells which belong inside the dog and which would usually be hidden away safely, well-protected by mucous.  In these situations, regardless of whether they are cancerous or not, spey or removal may be merited simply in order to prevent damage, pain and even perforation.  My second concern is as you suggest, that some of the possibilities for this lump may be malignant / cancerous (for example, adenocarcinomas).  If your vet is not certain in their own mind, then they will have a pathologist they can speak to who is used to seeing lumps such as this in the lab, and can guide them regarding the numbers and probabilities as to how many such lumps have neoplastic involvement.  Your vet will also be able to see the lesion in context and tell you how urgently any work needs to be done, which may turn out to be soon.

With apologies for unclear language:  'Neoplastic involvement' = 'cancer'

To clear up some terminology, there is a condition known as a vaginal polyp, which could well describe this lesion.  A vaginal polyp is where a smooth lump of overgrown vaginal tissue bulges from the vulva.  These can be due to a benign or malignant tumour as described above.  They can also change is size according to the oestrus cycle and treatment may be surgical.   I hope that something here helps.

In summary, this lump needs to be shown to your vet, and a spey may be recommended.