You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Treatment of estrogen receptor-positive breast cancer. Estrogen receptor (ER) expression is the main indicator of potential responses to endocrine therapy (ET), and approximately 70% of human breast cancers (BCs) are hormone-dependent and ER-positive. The introduction of adjuvant systemic therapy led to a significant improvement in post-surgical survival and a reduction in disease relapse, especially in women with early BC and those with ER+ tumors, who may receive ET alone or in combination with cytotoxic therapy. Adjuvant ET currently consists of (i) ovarian suppression, (ii) selective estrogen receptor modulators (SERMs) and down-regulators, and (iii) aromatase inhibitors (AIs). In patients with ER+ tumors pharmacologic ovary suppression with gonadotropin-releasing hormone agonists in combination with standard adjuvant therapy is generally more effective than adjuvant chemotherapy alone. Tamoxifen is the best established SERM, has favorable effects on BC control and bone metabolism, but also has adverse effects due to its estrogenic activity in other tissues. For these reasons, other SERMs have been developed. Fulvestrant is an ER down-regulator with several potential advantages over SERMs, including a 100-fold increase in its affinity for ER compared with tamoxifen and no estrogen-like activity in the uterus. The inhibition of the aromatase system with third-generation AIs is associated with improved survival in patients with advanced BC compared with SERMs. In postmenopausal patients with ER+ BC adjuvant treatment with AIs should be performed, either as sequential treatment after tamoxifen or as upfront therapy. Studies evaluating the role of AIs as first-line therapy are ongoing and the results are encouraging.
{"Chemical": ["Estrogen", "gonadotropin-releasing hormone", "Tamoxifen", "tamoxifen", "estrogen", "Fulvestrant"]}