Purpose: Little is known about the three-dimensional shape of breast cancer. Implicit to approaches that localize the center of the tumor for breast-conserving surgery (BCS) of non-palpable cancers is the assumption that breast cancers are spherical about a central point, which may not be accurate.
Methods: Pre-operative supine breast MRI images were obtained of 83 breast cancer patients undergoing partial mastectomy using supine MRI-guided resection techniques. Three-dimensional (3D) tumor models were derived after radiologists outlined tumor edges on successive MRI slices. Ideal resection volumes were determined by adding 1 cm in every dimension to the actual tumor volume. Geometrically defined parameters were used to define tumor shapes and associations between clinical variables and shapes were examined.
Results: Seventy-five patients had invasive cancer. Breast cancers were categorized into four tumor shapes: 34% of tumors were discoidal, 29% segmental, 19% spherical, and 18% irregular. If hypothetical spherical excisions were performed, non-spherical cases would excise 143% more tissue than the ideal resection volume. When the 3D shape of each tumor was provided to the surgeon during MR-guided BCS, the percentage of tissue overexcised in non-spherical cases was significantly less (143% vs. 66%, p < 0.001).
Conclusions: Information obtained from a supine MRI can be used to generate 3D tumor models and rapidly classify breast tumor shapes. The vast majority of invasive cancers and DCIS are not spherical. Knowledge of tumor shape may allow surgeons to excise breast cancer more precisely.
Keywords: Breast cancer; Breast shape; Breast-conserving surgery; Lumpectomy; MRI; Supine.