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It is not possible to tell about type of tumor from size because sometimes even small tumor are cancerous while big tumor can be non-cancerous.
One way of knowing what type of nodule you have is looking at BIRADS catagory of lesion.It is nothing but standard way of catagorizing finding of mammogram
in scale of 0-6
Category Diagnosis Number of Criteria
0 Incomplete Your mammogram or ultrasound
didn't give the radiologist
enough information to make a clear diagnosis; follow-up imaging is necessary
1 Negative There is nothing to comment on; routine screening recommended
2 Benign A definite benign finding; routine screening recommended
3 Probably Benign Findings that have a high probability of being benign (>98%); six-month short interval follow-up
4 Suspicious Abnormality Not characteristic of breast cancer
, but reasonable probability of being malignant (3 to 94%); biopsy
should be considered
5 Highly Suspicious of Malignancy Lesion that has a high probability of being malignant (>= 95%); take appropriate action
6 Known Biopsy Proven Malignancy Lesions known to be malignant that are being imaged prior to definitive treatment; assure that treatment is completed
If the lesion is suspicious,doctor will do Fine needle aspiration cytology to determine type of the nodule. So no need to worry.