This multicenter, two-cohort, non-randomized, open-label study will evaluate the safety and tolerability of assisted and self-administered SC Herceptin as adjuvant therapy in participants with early HER2-positive breast cancer following tumor excision. Participants will receive Herceptin 600 milligrams (mg) SC every 3 weeks for 18 cycles, either by an assisted administration using a conventional syringe and needle/vial formulation (Cohort A) or with assisted and self-administration using a single-use injection device (SID) in selected participants (Cohort B).