Trastuzumab administration associated with change in HER2 status.

Recent results from large randomized clinical trials have demonstrated that administration of trastuzumab reduces the risk of death by half in patients with early-stage breast cancer; however, controversy still exists as to the timing and duration of treatment with trastuzumab in the adjuvant setting and whether its administration should be continued after recurrence of disease. We present the unusual case of a patient with HER2/neu-positive stage I breast cancer who, after receiving adjuvant trastuzumab, relapsed to develop HER2/neu-negative metastatic disease.