Abstract 958: Signal transduction pathway activity of TGF-β and Hedgehog as possible response predictors to checkpoint inhibition in patients with advanced melanoma; a retrospective cohort study

Introduction: Although immunotherapy is highly effective in patients with melanoma, not all patients respond equally well to immune checkpoint inhibition (ICI). Preclinical data indicate that TGF-β pathway activity mediates immune evasion by tumor T cell exclusion and may therefore be predictive for response. Recently, a new mRNA-based methodology has been developed to measure and quantify signal transduction pathway (STP) activities in tissue. This study was initiated to characterize the STPs in advanced melanoma samples to better understand the role of STPs in immune check point efficacy.

Method: The OncoSIGNal pathway activity profiling PCR test (InnoSIGN) was used to measure the activity of 8 different STPs (AR, PI3K, MAPK, Hedgehog (HH), TGF-β, Notch, NFkB and JAK-STAT1/2) in biopsies (FFPE) from patients with advanced melanoma (n=34) and expressed on a scale from 0 -100. A biopsy of a metastatic site was obtained prior start of ICI therapy (nivolumab or pembrolizumab). These samples were analyzed for STP activity and related to progression-free survival (PFS). Also, STP activities were compared between responders (n=15; partial or complete response) and non-responders (n=19; defined as progression within 6 months).

Results: The mean HH score of responders versus non-responders was 35.7 + 6.1 vs 41.6 + 8.7 (p=0.038), while TGF-β scores were 53.9 + 6.2 vs 56.8 + 8.2 (p=0.265), respectively. Cox regression analysis showed a hazard ratio of 1-1.1 for PFS of both HH and TGF-β (HH: p=0.032) (TGF-β: p=0.071). Kaplan Meier curves indicated a better PFS for lower HH activity at a threshold of 46 (p< 0.001) and lower MAPK activity at a threshold of 47.3 (p= 0.041). No relation with PFS was detected for TGF-β activity. No statistically significant differences were observed in STP activity between different metastatic locations ((sub)cutaneous, lymph node or visceral metastases).

Conclusion: Signal transduction pathway activity of metastatic samples, taken prior start of ICI therapy, from patients with advanced melanoma, suggest that TGF-β did not correlate with response nor PFS but increased HH and MAPK STP activity may relate towards a worse PFS from ICI therapy.

Citation Format: Stefan G. vanRavensteijn, Daniele V. Taurello, Avital Amir, Yvonne J. Wesseling, Anne G. vanBrussel, Diederick M. Keizer, Henk M. Verheul, Kalijn F. Bol. Signal transduction pathway activity of TGF-β and Hedgehog as possible response predictors to checkpoint inhibition in patients with advanced melanoma; a retrospective cohort study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 958.

Abstract 6221: Support for targeted therapy selection in triple negative breast cancer patients using aberrant signal transduction pathway activity profiles

Introduction: Success of therapeutic interventions largely rely on the pathological and biological characteristics of the tumor and varies due to the heterogeneous nature of breast cancers. Triple negative breast cancers (TNBC) stain IHC negative for both hormone receptors (ER, PR) and HER-2. TNBC is usually treated with chemotherapy because of absence of any molecular target. This study is initiated to characterize TNBC based on a new methodology that measures and quantifies signal transduction pathways (STPs) activities to reveal potential tumor-driving STPs in TNBC and create new options for targeted therapy.

Method: Using the mRNA-based OncoSIGNal pathway activity profiling PCR test (InnoSIGN) STP activities of 7 pathways (AR, ER, PI3K, MAPK, HH, TGFβ and Notch) in 39 samples from normal breast tissue and 12 TNBC patients were quantified and expressed on a scale from 0-100. Normal healthy breast tissue was obtained from breast reduction surgery and areas where epithelial cells content was at least 50% were annotated and harvested for mRNA isolation and STP analyses. The normal STP activity is representing the normal physiological activity and is used as reference value. Aberrant high pathway activity in a patient tumor sample was concluded when this score was higher than twice the standard deviation above the mean of normal breast tissue STP activity.

Results: STP thresholds for interpretation of high aberrant activity were determined from 39 normal breast samples. Using these thresholds, STP activities in 12 TNBC samples were analyzed. In these TNBC samples, MAPK was in 75%, HH in 67%, PI3K in 58%, and AR, Notch and TGFβ were in 17% of the cases above the thresholds. In 50% of the cases a combination of MAPK and HH or a combination of PI3K and HH were found above thresholds. In 42% of the cases MAPK in combination with PI3K were above thresholds. Increased activity of AR was never observed in combination with increased HH activity.

Conclusion: By using the OncoSIGNal test high aberrant STP activities could be determined in TNBC patient samples. Results show that different pathways are aberrantly active, depending on the patient sample, which opens the opportunity for personalized targeted treatment of individual TNBC patients.

Next steps: The TNBC data set will be extended to further profile the STP activity in relation to different clinical outcomes and to investigate new opportunities for targeted therapies.

Citation Format: Diederick M. Keizer, Yvonne J. Wesseling, Dianne A. van Strijp, Saskia M. Vermeer, Eveline C. den Biezen. Support for targeted therapy selection in triple negative breast cancer patients using aberrant signal transduction pathway activity profiles [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6221.

Abstract P3-07-07: The use of ribociclib/letrozole combination as an alternative for neoadjuvant chemotherapy in selected patients with early luminal breast cancer

Introduction In hormone receptor-positive, HER2-negative early-stage breast cancer (BC), cyclin-dependent kinases 4 and 6 inhibition (CDK4/6i) in combination with endocrine therapy (ET) could represent an alternative to neoadjuvant chemotherapy (NAC). Methods NEOLBC is a randomized phase II trial that tailored neoadjuvant therapy in postmenopausal patients with early, luminal (ER >50%, PR any), HER2-negative, stage II/III BC based on the percentage of Ki67 positive cancer cells after a window of opportunity of two weeks letrozole. Patients with a Ki67 >= 1% after 2 weeks were randomized between ribociclib plus letrozole (RL) and chemotherapy (CT; AC-T regimen). The primary objective was to determine if RL gives a doubling in complete cell cycle arrest (CCCA; Ki67 < 1% on IHC) as compared to CT in the surgical specimen (70% vs. 35% of patients, respectively). Secondary endpoints included pathological response, toxicity and ER pathway activity (measured by the OncoSIGNal qPCR test). Results Out of 161 registered patients, 70 patients were randomized and 66 patients started treatment; 34 RL and 32 CT. Patient characteristics were equally distributed between the two groups, except for the PR status (RL 23.5% negative vs. 50.0% negative in the CT group). In the intention to treat analysis, the CCCA in the surgical specimen was similar for both groups: 35.3% in the RL vs. 31.3% in the CT group (p = 0.73). The pathological complete response (pCR) in the breast was not significantly different between the two groups (11.8% vs. 3.1%, p = 0.36) nor was the pCR rate in breast plus lymph nodes (8.8% vs. 3.1%, p = 0.61) for the RL vs. CT group, respectively. An explorative analysis on the difference in Ki67% (decline, no change, increase) from baseline to surgery showed a decline in 73.5% vs. 50.0%, no change in 17.6% vs. 31.3% and an increase in 8.8% vs. 18.8% of patients (p = 0.06) for the RL vs. CT group, respectively. In the RL group eight patients (23.5%) discontinued ribociclib early due to toxicity (two SAE’s were observed) vs. 10 patients (31.3%) discontinuing treatment in the CT group (one SAE was observed). Secondary endpoints, including the ER pathway activity analysis, will be presented in-depth during the meeting. Conclusion Although the primary endpoint was not met, the NEOLBC trial showed a similar CCCA and pathological response at surgery for RL vs. CT. Therefore, RL as an alternative for NAC merits further investigation in follow-up studies. ClinicalTrials.gov: NCT03283384

Citation Format: Anne Florine de Groot, Danielle Cohen, Joan B. Heijns, Caroline Mandigers, Diederick M. Keizer, Hein Putter, Elma Meershoek-Klein Kranenbarg, Marjolijn Duijm-de Carpentier, Kyra Dijkstra, Elise van Leeuwen-Stok, Gerrit-Jan Liefers, Sabine Linn, Judith Kroep. The use of ribociclib/letrozole combination as an alternative for neoadjuvant chemotherapy in selected patients with early luminal breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-07-07.

Inhibition of prostatic epithelial cell proliferation by a factor secreted specifically by prostatic stromal cells

Stromal cells from the prostate were recently shown to inhibit clonal growth of the prostatic carcinoma cell lines PC-3 (hormone-independent) and LNCaP (hormone-sensitive) in coculture. Our study revealed that stromal cell-conditioned medium strongly inhibited proliferation of PC-3 and LNCaP cells when grown in monolayer culture. Antiproliferative activity was found to be reversible, and was produced specifically by prostatic stromal cells and not by stromal cells derived from skin, foreskin, uterus, kidney, and Wilms' tumor. Inhibition was not species-specific, since the cell lines AT-2.1 and MATLyLu, derived from the Dunning rat prostate tumor, were also sensitive. No inhibition, however, occurred on breast and renal carcinoma cell lines, suggesting a prostate-specific action. The putative inhibiting factor(s) could be concentrated and partially purified by ammonium sulfate precipitation. The possible role in stromal control of epithelial cell proliferation is discussed.