This lump that you have may have different etiologies and cancer is a differential diagnosis. However, there are other explanations such as lumps from benign causes like fibroadenoma or fibrocystic disease which can have an accompanying infection producing this brown like discharge. Benign causes are also more common than the malignant ones.
I suggest you ask the radiologist about the BIRADS score of your mammogram. This will tell us if the findings are likely to be benign, malignant, or would need further tests such as a biopsy (http://biradsclass.blogspot.com to learn more about birads).
Regards and God bless.