Breast conserving surgery is possible when the cancer is small relative to the size of the breast, or where multiple cancers are grouped closely together. When the cancer is large (e.g. greater than 40% of the size of the entire breast), or when multiples cancers are found dispersed throughout the breast, then a mastectomy is more likely to be the appropriate procedure to safely remove the cancer/s.

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When the cancer is small (up to 20% of the size of the breast), the defect (or cavity) left in the breast after the cancer is removed is not expected to be significant. In these cases, a simple joining of breast tissue without reconstruction will suffice. Alternatively, an internal flap may be used to fill in the defect. When the cancer's size is between 20% to 40% of the entire breast, removing just the cancer without any reconstruction will leave a significant defect in the breast. This will lead to asymmetry between the breasts. In these cases, reconstruction via mammoplasty or chest wall perforator flaps may be appropriate.

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When breast conserving surgery is combined with radiotherapy, the risk of breast cancer returning to the breast is equivalent to that of a mastectomy and they are equivalent in terms of long term survival.

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Breast conserving surgery is becoming more commonly performed. Research indicates that patients who undergo breast conserving surgery attain higher satisfaction levels with their surgery compared to patients who undergo mastectomies, even mastectomies with reconstruction.