Herceptin - Does anyone know how long it takes to work?

My sister has been taking Herceptin since early December. Her blood markers for cancer are still increasing. Her MD told her not to worry but didn't say when she could expect any improvement.

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Answer:
Depends on many factors, such as whether being given as a single agent or with other drugs. Generally one likes to wait 6-8 weeks before making a call, and even then sometimes waiting longer is necessary. When treatment is first started, the disease is like a moving train, and it takes a while for it to stop. If she is not having other symptoms, then giving the treatment plenty of time to work is the key; rarely though does it take longer than 3-4 months to at least see stabilization–hopefully improvement will follow.

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Answer:
Tumour markers are not all that reliable. If she feels well I would agree with her doctor - don't worry about it. She's only been on herceptin for 2 months, the usual minimum course of treatment is a year, it is early days yet.