as your query there is no sign of breast cance..
it may be due to hormonal
changes and also its normal when you are sexual active.. it comes also when you aroused.
the another factors have to check for getting off your self from the fear of cancer..
1. any tumour in your breasts
2. any painless hard part
3. uneven shape - bad shape changes in your breast
4. inverted nipples..
do not to worry form breast cancer
and this problem will get off after some days..
check out all and wait and watch.. make yourself free from fear..
Dr. Nikul Patel
Ayurveda Sex Consultant