Warrior, none of the imaging modalities will give you absolute accuracy, they all have their own specific limitations. I remember the MRI indicated my mass was well over 2.5 cm. It was not detectable on either ultrasound or mammography. Final size was 1.3 cm Sometimes the MRI can pick up enhancement that isn't found upon final pathology. I wish I could give you a definitive answer, it seems like you have to wait ages to get that final pathology. My best to you.

My biopsy said the size was .8mm. The MRI said it was 2.1 cm. The doctor said that it might be swollen from the biopsy. The actual tumor was a little over 1 cm. I also plus 5 cm+ of DCIS that did not show up on any imaging.

Mine was 3 cm by diagnostic mammogram, 6 cm by MRI. Turns out the MRI picked up on a lot of other stuff in there that was precancerous and benign - we didn't realize that until pathology after surgery....

To get this back to the OP's question, it appears that Warrior73 is asking because she is undergoing neoadjuvant chemo and is hoping for a good response. This doesn't appear to be a question about screening mammograms or whether imaging can find a tumor.

Warrior, will you be having any screening done prior to surgery after you complete chemo? And are you asking so that you have an idea of how much the tumor was reduced by chemo, once you find out the tumor size after surgery? These days a lot of patients have neoadjuvant chemo, so this is probably a question that many people have. What is your diagnosis? Triple negative? HER2+? You might search the posts in the relevant forum to see how other people address the same question.

It would be helpful if you would include your diagnosis and treatment plan in your signature line. That's very useful information for those who are answering your questions.

This article addresses the issue of measuring the response to neoadjuvant chemo:

Direct comparison of PET/CT and MRI to predict the pathological response to neoadjuvant chemotherapy in breast cancer: a meta-analysis https://www.nature.com/articles/s41598-017-08852-8

"In conclusion, a limited number of head-to-head studies indicates that the diagnostic performance of MRI is similar to that of PET/CT for the assessment of breast cancer response to NAC. However, for monitoring breast cancer response to NAC, PET/CT is more sensitive than anatomic MR imaging, and PERCIST criteria may be more appropriate than RECIST criteria. Moreover, PET/CT is superior to MRI in assessing response at times between 1–3 cycles of NAC but not at time after 3 cycles of NAC. In the future, large-scale, head-to-head, well-designed trials are necessary to compare the predictive value and consider more factors (such as the definition of pCR and phenotype of breast cancer) of these two imaging techniques."

alice....mine was NOT found on screening mammography. It was found on diagnostic sonogram....that had been mistaken for three years on screening sonograms that accompanied my mammograms due to dense breasts.

It was missed. For. THREE. years.

alice...i corrected my earlier statement.