Cancer evolution results in the co-existence of multiple genetically distinct cancer cell populations within individual tumours. This is termed intra-tumour heterogeneity, recognised across different tumour types with dramatic implications for molecular profiling, which is currently done on a single sample of the tumour.

This information guides treatment choice but may not be representative of the diversity of the tumour. At the same time, inferences about cancer evolution are affected by intratumour heterogeneity because of sampling bias.  

At present the formalin-fixed residual surgical sample that is not paraffin embedded for diagnostic purposes is typically thrown away. Retention and homogenisation – ‘blending’– of this residual formalin-fixed leftover tumour tissue creates a more representative sample for analysis.

DNA may be extracted from this sample for sequencing - the 'RepSeq' approach. Our pilot RepSeq data, in kidney and other cancer type has demonstrated the potential of this methodology for robust mutational calling, accurate determination of cancer cell fraction and the ability to discern clonal from subclonal variants.  

Diagram showing the process for representative sampling and profiling of tumours.

In order to establish the feasibility of homogenization as a potential companion evolutionary and diagnostic tool, the HOLST-F study aims to 1) identify the proportion of primary tumour cases that have left over tissue amenable to homogenization across multiple tumour types and 2) pilot homogenization across multiple tumour types.  The molecular profile of the homogenate will be compared to that obtained from the diagnostic specimen using next generation sequencing techniques.
 
This is a prospective non-interventional study (NCT03832062). Patients undergoing surgical intervention at The Royal Marsden Hospital (NHS Foundation Trust) with leftover tumour tissue from primary breast, colorectal, gastric, pancreatic, ovarian, renal cancer and sarcoma surgeries, as well as melanoma lymph node dissections will be included in the feasibility assessment.  We aim to homogenise 500 cases across different tumour types. The study opened in September 2018 and is expected to run for 2 years.