The most usual ones are:

persistent itching and soreness
 

a lump or ulcer on the labia, possibly with a crust or discharge.
 

In some cases, before invasive cancer develops there will be pre-cancerous changes to the vulva. There may be white patches on the skin, and itching. Pre-cancerous changes may take place over several years and can be treated before they become more serious.

Remember that cancer of the vulva is a rare cancer. Problems such as itching can easily be caused by other conditions such as infections. However, you should always tell your GP about any symptoms that don’t clear up.