Why Mantoux Test Is Used?

hello doctor,
i have pain in my armpit since 15 days and now the lump has raised and its paining.I went to my family doctor and he gave me injection of Mantoux test on my arm.Now the area where injection is given becomes reddish and itching.Can you please tell me why doctor has given me injection of Mantoux test and what is necessity of Mantoux test? Is this any symptom of cancer?. I am girl of age 17. I am totally fit mu weight 60 and it is constant.