Sequencing of aromatase inhibitors

Hallmarks of aromatase inhibitor drug resistance revealed by epigenetic profiling in breast cancer

Aromatase inhibitors are the major first-line treatment of estrogen receptor-positive breast cancer, but resistance to treatment is common. To date, no biomarkers have been validated clinically to guide subsequent therapy in these patients. In this study, we mapped the genome-wide chromatin-binding profiles of estrogen receptor α (ERα), along with the epigenetic modifications H3K4me3 and H3K27me3, that are responsible for determining gene transcription (n = 12). Differential binding patterns of ERα, H3K4me3, and H3K27me3 were enriched between patients with good or poor outcomes after aromatase inhibition. ERα and H3K27me3 patterns were validated in an additional independent set of breast cancer cases (n = 10). We coupled these patterns to array-based proximal gene expression and progression-free survival data derived from a further independent cohort of 72 aromatase inhibitor-treated patients. Through this approach, we determined that the ERα and H3K27me3 profiles predicted the treatment outcomes for first-line aromatase inhibitors. In contrast, the H3K4me3 pattern identified was not similarly informative. The classification potential of these genes was only partially preserved in a cohort of 101 patients who received first-line tamoxifen treatment, suggesting some treatment selectivity in patient classification.

Development of new estrogen receptor-targeting therapeutic agents for tamoxifen-resistant breast cancer

Despite our deepening understanding of the mechanisms of resistance and intensive efforts to develop therapeutic solutions to combat resistance, de novo and acquired tamoxifen resistance remains a clinical challenge, and few effective regimens exist to treat tamoxifen-resistant breast cancer. The complexity of tamoxifen resistance calls for diverse therapeutic approaches. This review presents several therapeutic strategies and lead compounds targeting the estrogen receptor signaling pathways for treatment of tamoxifen-resistant breast cancer, with a critical assessment of challenges and potentials regarding clinical outcome. Medicinal chemistry holds the key to effective, personalized combination therapy for tamoxifen-resistant breast cancer by making available a diverse arsenal of small-molecule drugs that specifically target signaling pathways modulating hormone resistance. These combination therapy candidates should have the desired specificity, selectivity and low toxicity to resensitize tumor response to tamoxifen and/or inhibit the growth and proliferation of resistant breast cancer cells.

Optimal sequence of hormonotherapy in advanced breast cancer

PURPOSE OF REVIEW

Several active, well tolerated hormonal agents have become available in recent years for the treatment of patients with advanced, hormone receptor-positive breast cancer. When used in an appropriate sequential strategy, hormonal therapies offer the opportunity of prolonging disease control and maintaining quality of life. The widening use of aromatase inhibitors in the adjuvant setting, however, means that traditional sequential cascades must be revised. The review describes the most relevant evidence that can contribute to the optimal positioning of each agent in the sequence.

RECENT FINDINGS

Most recent phase II and III trials of hormonal therapy in advanced breast cancer have examined the role of exemestane, letrozole, anastrozole, and fulvestrant in postmenopausal women.

SUMMARY

Partial non-cross resistance between nonsteroidal (letrozole and anastrozole) and steroidal (exemestane) aromatase inhibitors may allow treatment with exemestane after a nonsteroidal aromatase inhibitor and vice versa. The estrogen receptor downregulator fulvestrant is also an option after treatment with aromatase inhibitors. The role of the progestin megestrol acetate and, paradoxically, of tamoxifen in the sequential strategy for advanced breast cancer is less well studied.

Overview and new strategies in metastatic breast cancer (MBC) for treatment of tamoxifen-resistant patients

The treatment with aromatase inhibitors (AIs) and fulvestrant has been demonstrated to be active in a proportion of tamoxifen-resistant breast cancer patients, obtaining, in some cases, a long-term control of tumor growth. Results from clinical trials indicate that treatment with fulvestrant might either precede or follow AIs. However, the AIs are now replacing tamoxifen as first-line advanced and adjuvant therapies, and thus, other options following tamoxifen failure are required. Fulvestrant may be effective in this setting, even if there is also evidence of a lack of cross-resistance between nonsteroidal and steroidal AIs, resulting in the potential use of steroidal AIs following nonsteroidal AI failure and vice versa. Resistance mechanisms to these therapies appear to be related to a cross talk between estrogen receptor (ER) and growth factor-signaling cascades. Novel therapeutic approaches for ER+ patients, which combine hormonal agents and signal transduction inhibitors, have been developed to overcoming resistance. Several trials are now investigating signal transduction inhibitors combined with endocrine agents. This approach might provide efficient treatments and delay the onset of antihormone resistance, thereby significantly improving patient's survival.

Novel perspectives for progesterone in hormone replacement therapy, with special reference to the nervous system

The utility and safety of postmenopausal hormone replacement therapy has recently been put into question by large clinical trials. Their outcome has been extensively commented upon, but discussions have mainly been limited to the effects of estrogens. In fact, progestagens are generally only considered with respect to their usefulness in preventing estrogen stimulation of uterine hyperplasia and malignancy. In addition, various risks have been attributed to progestagens and their omission from hormone replacement therapy has been considered, but this may underestimate their potential benefits and therapeutic promises. A major reason for the controversial reputation of progestagens is that they are generally considered as a single class. Moreover, the term progesterone is often used as a generic one for the different types of both natural and synthetic progestagens. This is not appropriate because natural progesterone has properties very distinct from the synthetic progestins. Within the nervous system, the neuroprotective and promyelinating effects of progesterone are promising, not only for preventing but also for reversing age-dependent changes and dysfunctions. There is indeed strong evidence that the aging nervous system remains at least to some extent sensitive to these beneficial effects of progesterone. The actions of progesterone in peripheral target tissues including breast, blood vessels, and bones are less well understood, but there is evidence for the beneficial effects of progesterone. The variety of signaling mechanisms of progesterone offers exciting possibilities for the development of more selective, efficient, and safe progestagens. The recognition that progesterone is synthesized by neurons and glial cells requires a reevaluation of hormonal aging.

Adjuvant systemic therapy for operable breast cancer

Breast cancer is the leading cause of cancer death in women in England and Wales. Systemic adjuvant therapy for breast cancer reduces recurrence and mortality both in early and advanced breast cancer. This review primarily looks at the role of adjuvant systemic therapy following surgery. Chemotherapy and hormonal therapy has changed dramatically in the last few decades with the advent of newer aromatase inhibitors and newer chemotherapy drugs like taxol. Monoclonal antibodies targeted against breast cancer cells like trastuzumab are gaining ground recently in the adjuvant settings. In this article we have reviewed the recent evidences for the appropriate adjuvant therapy in operable breast cancer.