Large Lumpectomy vs Unilateral Mastectomy

Hello everyone,

I am a 50-year-old woman recently diagnosed with stage 1A, grade 1, HER2-negative, hormone-positive breast cancer in my left breast. I had invasive ductal carcinoma confirmed in two locations. My genetic testing was negative for all cancer syndromes, and a sentinel lymph node biopsy showed no cancer.

Through lumpectomy, one small tumor (~4 mm) was successfully removed with clear margins. The second tumor which was in a different quadrant (also ~4 mm at maximum dimension side) could not be removed because the clip marking the biopsy site had shifted quite a bit, and the localization or surgical targeting missed the exact spot. There is a possibility that the biopsy itself already removed this focus, but pathology from the lumpectomy did not confirm the biopsy site in the tissue. A generous amount of tissue (roughly 10 times the diameter of the tumor) was removed, and a post-operative MRI now shows no visible cancer. Still, my surgeon recommends a second excision before proceeding with radiotherapy, to be certain that the area is addressed, which is frustrating.

At this stage, my options are:

• Larger lumpectomy with plastic surgery (tissue rearrangement, no implant): This could reduce the size of my left breast, possibly requiring reduction on the opposite breast for symmetry, followed by radiotherapy, hormone therapy, and long-term monitoring.
• Unilateral mastectomy with reconstruction: This could be nipple-sparing, with reconstruction done either immediately or later.

I never imagined that a small cancer would lead me on such an emotional rollercoaster. With limited knowledge about mastectomy, I am hoping to hear from those with medical expertise or personal experience. What are the real pros and cons of each approach, mostly the mastectomy since I am least familiar with? My main concern is that a large lumpectomy plus radiation may leave me with significant cosmetic changes, potential long-term side effects from radiotherapy on breast itself and other organs, increased chance of secondary cancer, and ongoing worry about recurrence. On the other hand, if mastectomy with reconstruction can provide peace of mind and manageable side effects, I would strongly consider it, provided that no radiation on the remaining tissue won't increase the chance of recurrence and hopefully no future complications exists due to the presence of implants—I heard that they are usually required to be replaced every 15 years at max.

For context, a second opinion from the tumor board of a major academic hospital recommended against a second excision, believing nothing would be found, and suggested moving forward with radiotherapy and monitoring or mastectomy if I really want the peace of mind and prefer to not take any chances. However, my surgeon who missed the focus on first try feels she can locate the area based on her sutures and the lumpectomy cavity and remove it with a generous margin if needed.

I would be so grateful for your thoughts, advice, or experiences—whether with lumpectomy or mastectomy—to help me see the bigger picture before making this decision. Thank you so much for your support, and apologies for the long message.

Thank you very much for your understanding and support.