A 45-year-old woman with HER2(-)/HER1(-) breast cancer underwent radical mastectomy, followed by radiation and chemotherapy. However, her symptoms progressed rapidly owing to meningitis carcinomatosa and she was fitted with a urethral catheter. She also had difficulty in walking. However, immediately after treatment with lapatinib, her symptoms almost completely disappeared. The catheter was removed and she no longer needed a wheelchair. Unfortunately, after treatment was stopped, the bilateral upper limb skin metastases reappeared, the brain metastases relapsed, and she again experienced symptoms of meningitis carcinomatosa. Lapatinib was restarted, resulting in an immediate improvement in the symptoms and a reduction in the skin and brain metastases. Immunohistochemical staining of the lapatinib-sensitive metastatic skin tumor showed it to be HER2(2+), FISH(-)/HER1(-). This result suggested that the lapatinib-sensitive lesions in the brain and meninges were also HER2-positive. Carcinomatosa meningitis has a very poor prognosis and no effective treatment has yet been developed. Here, we report the first case in which lapatinib has been used to effectively treat meningitis carcinomatosa in HER2(-)/HER1(-) relapsed breast cancer.
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