Available clinical data are inconclusive to support preferential use of aromatase inhibitors over tamoxifen in progesterone-receptor-negative and HER-2-positive tumors, but it was also clear that lower estrogen receptors, lower progesterone receptors, and positive HER-2 are associated with lower responsiveness to any type of endocrine therapy. Tumors overexpressing HER-2 are endocrine resistant and they require the blockage of the HER-2 pathway in addition to estrogen deprivation. Recent molecular studies have shown that endocrine responsiveness is to a large extent influenced by estrogen-receptor-related pathways. In the future, the key to the correct tailoring of hormone therapy will probably be the ability to subtype estrogen-receptor-positive breast cancer.
Repurposing is a drug development strategy that seeks to use existing medications for new indications. In oncology, there is an increased level of activity looking at the use of non-cancer drugs as possible cancer treatments. The Repurposing Drugs in Oncology (ReDO) project has used a literature-based approach to identify licensed non-cancer drugs with published evidence of anticancer activity. Data from 268 drugs have been included in a database (ReDO_DB) developed by the ReDO project. Summary results are outlined and an assessment of clinical trial activity also described. The database has been made available as an online open-access resource (http://www.redo-project.org/db/).
A specific systemic regimen cannot yet be recommended. Moreover, only a few data are available on which treatment selection can be based. Use of the existing cytotoxic agents can be optimized for this patient subgroup by investigating the proliferative signals and the suitability of these signals as therapeutic targets, besides assessing the BRCA1-pathway in this subgroup as regards treatment. A greater understanding of the pathologic and molecular characteristics of this phenotype may lead to customized treatment for these patients.
Selective phosphodiesterase 5 inhibitors, including sildenafil, tadalafil and vardenafil, are widely-used in the treatment of erectile dysfunction and pulmonary arterial hypertension. They are also well-known as examples of successful drug repurposing in that they were initially developed for angina and only later developed for erectile dysfunction. However, these drugs may also be effective cancer treatments. A range of evidentiary sources are assessed in this paper and the case made that there is pre-clinical and clinical evidence that these drugs may offer clinical benefit in a range of cancers. In particular, evidence is presented that these drugs have potent immunomodulatory activity that warrants clinical study in combination with check-point inhibition.
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