Vulva cancer query?

My mum had a biopsy and was called in to receive her results , on the day she was told she has cancer of the vulva and today she has received a letter , I was wondering if you can give me an in depth explanation of the letter. 

It states “her biopsy has confirmed a well differentiated squamous cell carcinoma arising in VIN 3. 

We are not entirely sure what this means. 

Thankyou for any information you can give