I've a small round bump under the surface of the skin on my breast since 1 month. the skin on top is brownish & the bump can be seen. it's immobile & feels soft/firm. i'll call my gp, but i'd like to know if cancer is likely with such characteristics?

It is a good idea to see a doctor. Cancer is unlikely. You can reduce your risk of cancer by adopting healthy habits: Eat a mostly vegetarian diet, avoid alcohol, tobacco and street drugs, avoid excessive exposure to sun, maintain healthy weight, get HPV vaccine, exercise 30 minutes each day, drink enough water so your urine is mostly colorless. Wish you good health!