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Tamoxifen has been used in patients with estrogen - sensitive breast cancer , yet resistance to antiestrogens and recurrence will appear in some of the patients after its continued use .
 Tamoxifen, estrogen
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Tamoxifen, estrogen