The Oncotype DX AR-V7 Nucleus Detect test is the first and only nuclear-localized assay to identify patients who will not respond to androgen receptor (AR)-targeted therapy (like abiraterone (Zytiga®), enzalutamide (Xtandi®) and apalutamide (Erleada®) and should receive chemotherapy or other therapies instead.2-5 By identifying AR-V7 protein in the nucleus of circulating tumor cells (CTCs), the AR-V7 Nucleus Detect test eliminates false positives and detects resistance to AR-targeted therapies with unparalleled specificity.4
How AR-V7 causes resistance to AR-targeted therapies
Tumors can adapt (and become resistant) to AR-targeted treatments. One of the most common adaptations is AR-V7—a protein variant of the androgen receptor. This splice variant is constitutively active and it lacks the ligand binding domain, which is critical for the effectiveness of AR-targeted therapies. Patients with nuclear AR-V7 protein receive no benefit from AR-targeted therapies, but may still respond to taxane chemotherapy.1-6
AR-V7 is a splice variant of the androgen receptor (AR) that lacks the ligand binding domain2
AR-V7 variants are resistant to arbiraterone and enzalutamide1,3,4
The percentage of patients with AR-V7 in the nucleus (nuclear AR-V7+ patients) increases with exposure to multiple therapies including AR-targeted therapies2:
- Roughly 1 in 5 patients (18%) are nuclear AR-V7+ after receiving one round of therapy.
- Roughly 1 in 3 patients (31%) are nuclear AR-V7+ after receiving two rounds of therapy.
Why nuclear localization eliminates false positives
The AR-V7 Nucleus Detect test detects protein in the nucleus of circulating tumor cells (not cytoplasmic AR-V7)—making it more specific than assays that do not localize AR-V7 identification.
Studies show that AR-V7 protein found in the nucleus of CTCs is an absolute indicator of resistance. Although AR-V7 proteins are also found in the cytoplasm, transcription of tumor growth genes occurs in the nucleus.3 In addition, some AR-V7 protein does not translocate to the nucleus; and some mRNA does not translate into protein.3 As a result, nuclear localization of the AR-V7 protein is important to avoid the potential for false positives.
- 1 Cytoplasmic AR-V7 translocates into the nucleus
- 2 Nuclear AR-V7 binds to DNA
- 3 Transcription of tumor growth genes
- 4 Translation of tumor-growth gene mRNA into protein