Which Part of the Sample Should Be Analyzed
When assessing pathological specimens, particularly in oncology and neoadjuvant therapy settings, multiple spatially distinct samples should be obtained from different regions of the tumor and surrounding tissue, with precise documentation of their anatomical location using neuronavigation or stereotactic techniques.
Spatial Sampling Requirements
The most critical principle is that samples must be obtained from multiple distinct anatomical regions rather than a single location, as tumors demonstrate significant spatial heterogeneity 1, 2.
Specific Sampling Locations
For tumor specimens, particularly in neoadjuvant settings, samples should be systematically obtained from:
- Tumor core (including necrotic areas when present)
- Contrast-enhancing tumor portions on imaging
- Non-contrast-enhancing presumed tumor areas (T2/FLAIR hyperintense regions)
- Immediately adjacent macroscopically unaffected tissue when clinically safe 1
At least two samples per respective MRI abnormality should be obtained, positioned as distant from each other as possible to account for spatial intratumoural heterogeneity 1.
Documentation and Orientation
Critical Documentation Requirements
The precise location and contrast enhancement status of each sample must be electronically documented using intraoperative neuronavigation systems or stereotactic biopsy techniques 1. This spatial mapping is essential because:
- It allows correlation between histological findings and imaging characteristics
- It enables accurate assessment of treatment response in different tumor regions
- It facilitates research on spatial heterogeneity
Timing Considerations
Samples should be obtained early during resection to minimize anatomical distortions from brain shift on neuronavigation 1. For large anatomical resections, specific documentation of sample orientation and margins must be performed to correlate samples with their respective MRI locations 1.
Sample Size and Representation
For Proficiency Testing
When the goal is quality assurance or concordance assessment, the sample size refers to different entities depending on what is being monitored 3:
- For overall concordance: total number of cases (positive and negative combined)
- For sensitivity monitoring: number of true-positive cases only
- For specificity monitoring: number of true-negative cases only
For Pathological Response Assessment
In renal cell carcinoma and other solid tumors post-neoadjuvant therapy, systematic transverse sectioning at regular intervals (typically 5mm) is recommended, with at least one section per centimeter of maximum tumor dimension submitted for microscopic examination 2.
Special Considerations
Recurrent Disease
In the recurrent setting, samples should particularly target actively growing tumor as suspected from imaging to enhance the probability of sampling viable tumor 1. Documentation should note whether the recurrent lesion is in-field versus out-of-field, or local versus distant recurrence 1.
Research Tissue Preservation
When tissue is needed for both clinical assessment and research:
- Punch biopsies taken before fixation represent a low fraction of total area and minimally affect residual tumor assessment 2
- Alternatively, samples can be taken from the rear face of tissue slices not used for standard sectioning 2
- Photographs or sketches of research sampling locations should be maintained in the research database for later mapping 2
Common Pitfalls to Avoid
- Sampling only one region: This fails to capture tumor heterogeneity and may miss areas of viable tumor or treatment response
- Delayed sampling: Waiting until late in resection allows brain shift to compromise neuronavigation accuracy 1
- Inadequate documentation: Failing to record precise anatomical locations prevents meaningful correlation with imaging and limits research utility
- Ignoring non-enhancing regions: These areas may contain significant tumor cellularity despite lack of contrast enhancement 1
The key principle is that "which part of the sample" is not a single answer but rather a systematic approach to obtaining multiple representative samples from all relevant tumor regions with precise spatial documentation.