On September 14, 2022 Sermonix Pharmaceuticals Inc., a privately held biopharmaceutical company developing innovative therapeutics to specifically treat ESR1-mutated metastatic breast and gynecological cancers, reported shared a case report detailing the first-ever known finding of a durable complete response that could be characterized as complete clinical remission in a metastatic estrogen receptor-positive (ER+)/HER2- breast cancer patient with an ESR1 mutation after prior CDK4/6 inhibitor treatment upon participation in any single-agent hormonally based therapy (Press release, Sermonix Pharmaceuticals, SEP 14, 2022, View Source [SID1234619585]).

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The case report, "Durable Complete Remission of Metastatic ER+/HER2- Breast Cancer After Lasofoxifene Therapy," was initially shared Sept. 9 at the ninth-annual Metastatic Breast Cancer Research Conference in Park City, Utah. Lasofoxifene is Sermonix’s lead investigational drug.

The durable complete response (CR) was reported during Sermonix’s Phase 2 Evaluation of Lasofoxifene in ESR1 Mutations (ELAINE 1, NCT03781063) study. The open-label, randomized study evaluated the efficacy of oral lasofoxifene versus intramuscular fulvestrant for the treatment of postmenopausal women with locally advanced or metastatic ER+/HER2- breast cancer with an ESR1 mutation and progression-free survival as the primary endpoint. Top-line ELAINE 1 data was presented Sept. 10 during the European Society for Medical Oncology (ESMO) (Free ESMO Whitepaper) Congress 2022 in Paris. Although not statistically significant, the results of the study numerically favored lasofoxifene.

The patient was recruited to the ELAINE 1 study and started treatment on Dec. 16, 2020. Her first radiological assessment, eight weeks after lasofoxifene initiation via PET-FDG scan, revealed no pathological uptake in her pleural lesions, a sum diameter of 14 mm (55% reduction) and significant reduction of the bony lesion in the ilium with no new pathological findings. Scans at Week 16 revealed further improvement up to complete radiological disappearance of all measurable and non-measurable lesions. Radiological complete response was maintained at 80 weeks (June 29, 2022).

"Achieving a complete response in metastatic breast cancer with endocrine treatment post CDK4/6 inhibitor is exceedingly uncommon, particularly with single-agent endocrine therapy," said Dr. Einav Nili Gal-Yam, M.D., Ph.D., ELAINE 1 principal investigator and head of the Breast Oncology Institute at Chaim Sheba Medical Center in Ramat Gan, Israel. "This is a very gratifying result, pointing to lasofoxifene’s potentially significant role in addressing the unmet needs of patients with ESR1 mutations. We look forward to the continued clinical development of this drug."

About Lasofoxifene
Lasofoxifene is an investigational, nonsteroidal selective estrogen receptor modulator (SERM), which Sermonix licensed globally from Ligand Pharmaceuticals Inc. (NASDAQ: LGND) and has been studied in previous comprehensive Phase 1-3 non-oncology clinical trials in more than 15,000 postmenopausal women worldwide. Lasofoxifene’s bioavailability and activity in mutations of the estrogen receptor could potentially hold promise for patients who have acquired endocrine resistance due to ESR1 mutations, a common finding in the metastatic setting and an area of high unmet medical need. Lasofoxifene’s novel activity in ESR1 mutations was discovered at Duke University and Sermonix has exclusive rights to develop and commercialize the product in this area. Lasofoxifene, a potent, oral SERM could, if approved, play a critical role in the targeted precision medicine treatment of advanced ER+ breast cancer.