What happened, in summary

This 38-year-old woman with no relevant medical history was diagnosed with de novo Stage IV breast cancer in the left breast. Tumor testing showed ER 90%, PR 70%, and HER2 IHC 3+. Imaging found 1 small pelvic lesion, and her team treated the disease with curative intent. She received 6 cycles of neoadjuvant docetaxel, carboplatin, trastuzumab, and pertuzumab, followed by left mastectomy. Pathology showed residual cancer burden 2, meaning moderate residual disease, so adjuvant T-DM1 was started to continue HER2-directed therapy. Port placement had been repeatedly discussed, but she declined, so the first T-DM1 infusion was given through a peripheral IV. This access decision became important because T-DM1 can cause significant local tissue injury if it leaks outside the vein. About 80 minutes into the infusion, the medication was found to have infiltrated into surrounding tissue. The infusion was stopped, and she was observed for 90 minutes with home instructions for compresses, avoiding friction, and monitoring the area. One week later, the site was extremely painful and blistering, with spread beyond the original marking. Dermatology confirmed a direct toxic effect from extravasated chemotherapy. Treatment included cefadroxil, clobetasol ointment, gabapentin for pain, high-dose weekly vitamin D, cold compression, and close wound care. At about 3 weeks, itching remained significant, so tacrolimus ointment was added. By about 4 weeks, the wound was nearly healed and pain-free, with residual hyperpigmentation. She then consented to port placement and received the remaining T-DM1 doses through the port during wound healing. Her immediate course centered on safely continuing HER2-directed treatment while managing pain, itching, blistering, and infection prevention from the extravasation injury.