Interstitial lung disease is a rare complication of trastuzumab-based breast cancer treatment with few case reports published. Herein, we report the case of a 67-year-old female with early-stage HER2-postitive breast cancer who developed interstitial pneumonitis during cycle 5 of treatment with trastuzumab combined with carboplatin and docetaxel. After supportive care and treatment with prednisone, the patient showed rapid improvement of respiratory symptoms. Retreatment with trastuzumab as a single agent led to worsening of symptoms and required a second course of treatment with prednisone combined with cyclophosphamide, which was followed by improvement of symptoms. In conclusion, interstitial pneumonitis is a rare but life-threatening adverse event from trastuzumab breast cancer treatment.

Breast cancer is the most common tumor among women, and approximately 6% of the patients have de novo metastatic breast cancer. Occult breast cancer accounts for only 0.1–0.8% of the cases and most commonly presents with axillary lymphadenopathy. Scalp metastases are rare and have been described as a sign of progression or widespread metastatic disease. Here, we describe a rare case of de novo metastatic breast cancer to the scalp as the single site of spread and without an identifiable primary breast tumor.