Hello and thanks for posting,

Carcinoma does mean cancer but in situ describes a very early form of the disease - it means the cancerous-looking cells are only seen where they started in the outermost layer of the skin and aren't growing deeper underneath.  

The British Association of Dermatology (BAD) has a patient leaflet about squamous cell carcinoma in situ (Bowen's disease) at this link and about actinic keratosis here.

Hopefully, the cream you have been given will sort everything out. 

Please give us a call if you want to talk anything over.  Our number is Freephone 0808 800 4040 and we are around from 9-5 weekdays,

Wishing you the best, 

Julia