A 42-Year-Old Woman Is Evaluated Because She Has Noticed a Thickening

A 42-year-old woman is evaluated because she has noticed a thickening in her left breast over the past few weeks. She noticed it a few months ago, but because it seems to come and go, she put off seeking medical attention. She is premenopausal. She had menarche at age 13 years. When she was 35 years, she had one child (whom she breast-fed) after a normal first full-term pregnancy. She took oral contraceptives for 10 years before her pregnancy. She has no known radiation exposure and no family history of breast cancer. On physical examination, there appears to be some asymmetry in breast tissue density in the upper outer quadrant of the left breast compared with the right one, but no discrete mass. There are no palpable lymph nodes. Results of a mammogram are negative. What would be the most appropriate next step in this patients management?

A) Breast ultrasound; consultation with a surgeon experienced in breast diagnosis
B) Reassurance that because her family history is negative and the mammogram is negative, no additional studies or treatment is required
C) MRI of the breast
D) Measurement of circulating tumor markers, including CA15-3 and carcinoembryonic antigen A 68-year-old woman is