Radical Mastectomy: Surgical Removal of the Entire Mammary Gland from a Mouse to Study Cancer Progression

1. Mastectomy

NOTE: The timing of the mastectomy is very important. If it is done too early, lung metastasis does not occur. If it is done too late, the primary tumor has invaded major blood vessels, which make a complete oncologic resection challenging. Thus, multiple time points were tested for mastectomy to determine which time point produced the appropriate balance in waiting for metastasis before resection became too challenging. After doing so in over 50 mouse experiments, it was demonstrated that mastectomy at 8 days after cancer cell inoculation (or when the tumor size reaches 5 mm) was the ideal time point to achieve that balance.

1. Anesthetize a mouse with 2-4% isoflurane and 0.2 L/min oxygen flow until the mice breathe calmly (2–3 min) and inject 0.05 mg/kg buprenorphine into its shoulder subcutaneously.
2. Restrain the mouse’s limbs using lab tape and sterilize its skin using chlorhexidine, iodine, and 75% ethanol, using cotton swabs.
3. Make a 5 mm skin incision 2 mm to the left from the surgical scar that was made at the initial cancer cell inoculation, using the microdissection scissors. Extend the incision toward the root of the forelimb to remove the tumor, the skin including the surgical scar, and the lesion in contact with the tumor, as well as the axillary lymph node basin in which most of the time no visible lymph node exists at the time of the mastectomy. Make sure not to damage the axillary vein.
4. Close the skin defects by stitching, using sterile 5-0 non-absorbable sutures in the shape of a “Y”.
5. Return the mouse to a clean cage and monitor until they have recovered and are moving freely (after ~1–2 min). If an animal does not appear to be in good health within 24 h of surgery, administer buprenorphine (0.2 mg/kg).
6. Remove the sutures under anesthesia (with 2-4% isoflurane and 0.2 L/min oxygen flow) 7 days after surgery.