The fact that you are BRCA negative is a plus, but not a guarantee against cancer, but it does decrease the chances. However, the ultrasound can usually tell you if the cyst appears to be cancer or not. Based on the fact that your doctor prescribed you birth control pills to reduce the size of the cyst, my guess is that the ultrasound was not too suspicious for cancer. Waiting to see if it resolves is probably an option that you could discuss with your doctor, and surgery is also an option. It mostly depends on how bad your symptoms are, and how suspicious the cyst appears for cancer. Also, if the cyst is very large or continues to persist, that might warrant surgery as well. I hope this answers your question. Please let me know if you have any moire questions.