The importance of assessing the heterogeneity of cancer
The cell is the basic structural, functional and biological unit of all living organisms. For years, pathologists have articulated the importance of “chemistry in context,” regarding the concept of visualizing protein expression in context to the cell. Recently, the concept of branched evolution was articulated, which suggests that some tumors are molecularly heterogeneous.
The blood provides the perfect medium to measure tumor heterogeneity through the analysis of single tumor cells shed into circulation, which can provide understanding of heterogeneity not only from single tumor sites but of all metastatic tumor sites contributing to tumor burden.
In collaboration with oncologists at Memorial Sloan Kettering Cancer Center, metastatic castration-resistant prostate cancer (mCRPC) patient blood was assessed with Epic’s CTC technology to characterize patients with four common drivers of mCRPC disease progression:
- AR and PSMA protein expression
- AR protein subcellular localization
- ERG gene rearrangements
- PTEN genomic deletions
Expression and localization of AR may help in the prediction of benefit from androgen receptor targeting therapies. PSMA is associated with androgen independence and progressive patients. Alterations in the ERG & PTEN genes are associated with progressive disease and associated with reciprocal feedback of androgen signaling. ERG/PTEN alteration status may also help to identify patients who could respond to combination trials with PI3K/AKT inhibitors.
Our analysis demonstrated a high level of heterogeneity seen at the single cell level for both protein expression and protein localization confirming the importance of a highly sensitive CTC-detection platform and discrete multiplexed single cell analysis.
AACR-PCF Abstract #A11: Frequency and characterization of circulating tumor cell (CTC) populations in metastatic castration-resistant prostate cancer (mCRPC)
Androgen Receptor (AR) Localization
Figure from Abstract #A11 showing CTCs characterized with AR (blue dots), PSMA (red dots), PTEN (red is a deletion) & ERG (red is a rearrangement) characterization from a single blood sample compared to known cell line controls. Bottom chart identifies the AR subcellular localization and percentage of CTCs that are either AR nuclear, AR both nuclear & cytoplasmic, AR cytoplasmic, or AR negative. An association between number of systemic therapies treated and increase AR localization heterogeneity was identified.
Additionally, the platform was shown to provide higher detection rates of CTCs as compared to the FDA approved CellSearch® platform. Epic’s CTC technology detected >5 traditional CTCs per tube of blood in 93% of 41 patient samples and >5 of any CTC subtype per tube in 100% of patients, whereas the CellSearch® platform detected traditional CTCs in only 56% patient samples.
GU14 Abstract #132: Molecular characterization of circulating tumor cells (CTC) and CTC subpopulations in progressive metastatic castration-resistant prostate cancer (mCRPC).
Figure from Abstract #132 highlighting the sensitivity of Epic CTCs compared with matched blood samples run with CellSearch® CTCs
Summary:
Intra- and inter- tumor heterogeneity is common and can be visualized through the single cell protein and molecular characterization of CTCs using the Epic platform. In a single patient blood draw, we detected CTCs in 41/41 (100%) of mCRPC patients and successfully characterized the CTCs for AR & PSMA protein expression, AR protein subcellular localization and ERG & PTEN genomic alterations.
Heterogeneity of prostate cancer biomarkers in the CTCs correlated with more progressive patients suggesting relevance to the importance of a real-time biopsy to assess tumor cell selection and evolution. We will continue to expand our morphologic, protein, and molecular characterization methods to develop signature for patient selection and assessment of mechanisms of drug response and resistance.
Read the next blog post from GU14 + AACR-PCF:
Real-time tumor biopsying: towards a future of oncology pharmacodynamics (PD) monitoring and detection of aggressive transformation