Low NR2F1 Expression May Predict Risk of Metastatic Breast Cancer

Julio Aguirre-Ghiso, PhD

Low NR2F1 expression in disseminated tumor cells (DTCs) that is found in bone marrow may be indicative of developing metastatic breast cancer, according to results of a study published in Breast Cancer Research.

In the study, zero or low levels of the protein identified in bone marrow were associated with metastasis and poor survival, whereas patients who harbored high levels of the protein demonstrated longer disease-free intervals (DFI) and no evidence of metastatic disease.

"This research shows that the survival advantage in these patients is due to high levels of this protein. Tests using this protein marker could further improve curative treatment of breast cancer, sparing patients from unnecessary treatments,” lead researcher Julio Aguirre-Ghiso, PhD, director of Solid Tumor and Metastasis Research at The Tisch Cancer Institute, Mount Sinai Health System, said in a news release. “Identifying patients with disseminated disease that is not yet symptomatic and characterizing it for potential dormancy or metastatic recurrence is a game changer."

In the study, researchers pooled patient data from 3 clinical trials conducted between 1997 and 2008—– Oslo1, NeoTax, and SATT. The NeoTax trial enrolled 260 patients with stage III/IV breast cancer between 1997 and 2003; stage IV patients were limited to those with T3/T4 and/or N2/N3 disease with distant metastases. The Oslo1 trial accrued 920 patients with stage I/II breast cancer between 1995 and 1998, and the SATT study included 1121 patients with surgically resectable disease between 2003 and 2008.

Researchers assessed NR2F1 expression in patients with DTC-positive breast cancers by double immunofluorescence in the bone marrow, of which 13 were pulled from Oslo1, 38 from NeoTax, and 35 from SATT.

NR2F1^high and NR2F1^low cells were defined as circular signals around the nuclear area and absence or presence of up to 5 small signals on immunostaining, respectively. A NR2F1^high staining was representative of >5 small signals, ≥1 large signals, or the presence of signal clusters. Samples with ≥50% NR2F1^high DTCs were termed “dormant” and samples with <50% NR2F1^high DTCs were termed “non-dormant.”

Results showed that patients who experienced systemic relapse within 12 months after treatment harbored NR2F1^low (≤1% NR2F1^high DTCs) in their bone marrow, whereas half of patients who had undergone serial sampling and demonstrated no relapse at follow-up had ≥50% NR2F1^high DTCs in their last bone marrow assessment.

Among the 18 relapse-free patients at the time of their last DTC-positive bone marrow assessment, distant DFIs favored patients who harbored ≥50% NR2F1^high DTCs versus those with NR2F1^low DTCs (log-rank, P = .007).

Distant DFI was defined as survival with no evidence of distant breast cancer recurrence or breast cancer death. Findings were modeled with Kaplan-Meier curves and coupled with log-rank test P values.

Of the patients with NR2F1^low DTCs, 90% had or experienced systemic relapse or breast cancer death and 67% revealed bone metastasis. Similar findings were reported for patients who carried ≤1 NR2F1^high DTCs. Conversely, 57% of patients who carried ≥ 50% NR2F1^high expressing DTCs, had or experienced systemic relapse and only 29% indicated bone metastasis.

However, a survival difference was reported by classification according to Ki67-expressing DTCs (P = .520). Moreover, a survival analysis of all nonmetastatic patients at the time of last DIF DTC-positive bone marrow aspiration showed a difference in distant DFI (P = .023).

"Improved techniques to assess the population of patients with residual disease and their dormant or reactivating state will be key to identifying the risk of future metastasis despite undergoing standard treatment,” said Aguirre-Ghiso. “This opens the way for testing new treatments that prevent metastasis by inducing dormancy or eradicating the dormant disseminated cancer cells that have not yet initiated metastatic growth."

Borgen E, Rypdal M, Soledad Sosa M, et. al. NR2F1 stratifies dormant disseminated tumor cells in breast cancer patients [published online October 16, 2018]. Breast Cancer Res. doi: 10.1186/s13058-018-1049-0.