In more detail how the timing of the genetic testing (pre-treatment vs post-treatment) might impact the information...

Based on the provided guidelines, here's an explanation of genetic testing timing considerations:

According to the NCCN Guidelines, there are two distinct types of genetic testing that happen at different times for different purposes:

1. Diagnostic Genetic Testing (At Diagnosis):

• This testing looks specifically at the cancer cells from your blood or bone marrow samples
• According to the guidelines, this should be done before starting treatment to:
  • Help determine your specific type of colorectal cancer
  • Guide treatment decisions
  • Look for specific mutations that may affect treatment choices

1. Hereditary/Predisposition Testing: The NCCN Guidelines note that if testing for inherited genetic risk is needed, timing matters because:

• Testing blood during active disease will show the genetic changes of the leukemia
• A skin punch biopsy may be needed to get DNA that hasn't been altered by the cancer
• Blood or saliva testing can be done once in remission when cancer cells are gone

As stated in the guidelines: "While it can be confusing, just know that testing done to look for an inherited gene (germline) mutation or an inherited risk of cancer is different than genetic testing done specifically on cancer cells or testing to look for proteins produced by cancer cells."

The guidelines recommend discussing timing with your care team since some testing needs to be done before treatment starts to guide therapy choices, while other testing can wait until after treatment has begun or even until remission.

Sources:

• NCCN Guidelines for Patients: Acute Lymphoblastic Leukemia, 2023
• NCCN Guidelines sections on "Genetic risk testing" and "Genetic and biomarker testing"

I encourage you to discuss the specific timing of different genetic tests with your healthcare team as they can best determine the optimal sequence based on your individual situation.