Co-Chairs Kurt A. Schalper, MD, PhD, and Vamsidhar Velcheti, MD, prepared useful Practice Aids pertaining to solid tumor for this CME/MOC activity titled “PATHway to Decoding the Impact of Cancer Immunotherapy: Latest Advances in Biomarker Testing and Pathologic Response Assessment.” For the full presentation, downloadable Practice Aids, and complete CME/MOC information, and to apply for credit, please visit us at https://bit.ly/3SsmiMV. CME/MOC credit will be available until February 14, 2025.

1. IASLC Multidisciplinary Recommendations
for Pathologic Assessment of Lung Cancer
Specimens Following Neoadjuvant Therapy1
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Recommendation 1
The term tumor bed is the area where the original pretreatment tumor was considered to be located. It can be
challenging to determine whether necrosis and stromal inflammation and/or fibrosis are due to regression secondary to
neoadjuvant therapy, native tumor characteristics, or a combination. For this reason, we favor the term tumor bed. It is
suggested to simply describe the major components of the tumor bed: (1) viable tumor, (2) necrosis, or (3) stroma
(which can include inflammation or fibrosis). See page 3 for an example.
Recommendation 2
It is essential that information be provided from the surgical team to the pathology laboratory on whether the patient
received neoadjuvant therapy, in order for this specimen processing protocol to be followed. If there is more than one
tumor in the specimen, it is of critical importance to also provide this information. It is good clinical practice to correctly
label the specimen with the lobe(s) resected and to clarify any issues that may be needed for pathologic staging such
as the pericardium, diaphragm, or chest wall.
Recommendation 3
Lung cancer resection specimens following neoadjuvant therapy should be sampled to optimize the comprehensive gross
and histologic assessment of the lung tumor bed for pathologic response. The tumor should be cut in its greatest
dimension to maximize the tumor bed cross section. In cases where identification and/or orientation of the tumor are
difficult, review of the preoperative CT scan can be helpful. Tumors 3 cm or less in size should be completely sampled.
For larger tumors, greater than 3 cm, the tumor should be cut across in serial sections 0.5-cm thick, and after gross
inspection, the most representative cross section showing viable tumor should be sampled. At least one cross section
of the entire tumor (0.5-cm thick) with a gross photograph and histologic mapping should be made. Histologic sections
at the tumor periphery should include 1 cm of adjacent lung parenchyma. Pathologic response cannot be assessed in
small biopsies; a resection specimen is required.
Recommendation 4
To determine the border of the tumor bed, the edge of the tumor needs to be distinguished from the surrounding
non-neoplastic lung parenchyma. This can be facilitated by a review of the gross specimen and the histologic slides
from the periphery of the tumor bed.
Recommendation 5
Determination of the pathologic response to therapy should be made after review of all H&E slides of tumor by
estimating the percentages of (1) viable tumor, (2) necrosis, and (3) stroma, which includes both fibrosis and
inflammation. Each of these three components add up to 100%. Each component should be assessed in 10%
increments, unless the amount is below 5% when an estimate of single percentages should be recorded. While this
is primarily done by the review of histologic sections of the tumor bed, correlation with the gross findings, in some cases
facilitated by a gross photograph, may be important in markedly necrotic and/or cavitated tumors where it is not
possible to reflect this change in histologic sections.
Note: Although it may be useful to record the amount of each component on each individual histologic slide,
it needs to be kept in mind that the amount of tumor bed varies on each slide, so these percentages cannot be summed
and averaged as if they were in equal amounts. This is a semiquantitative process. There is no validated quantitative
method that is available that can be implemented in a timely fashion for clinical decisions.
A proposed synoptic template for reporting pathologic findings for resected lung cancers following neoadjuvant therapy
is summarized on page 2.

2. Recommended Synoptic Template for Recording
Lung Cancers Following Neoadjuvant Therapy
This page has been designed for your use. Please feel free to print and use it in your practice.
Primary tumor
Type of neoadjuvant therapy
• No known presurgical therapy: _____
• Type of neoadjuvant therapy
– Chemotherapy: ____________________
– Radiotherapy: ____________________
– Immunotherapy (please specify): ____________________
– TKI (please specify): ____________________
– Other (please specify): ____________________
Treatment effect in primary tumor
• Percentage of viable tumor (record in 10% increments except below 10%; then record single digits between 1%-5%): _____
• No residual viable tumor identified: _____
• Percentage of necrosis: _____
• Percentage of stroma (includes fibrosis and inflammation): _____
Grade of inflammation (choose the appropriate grade)
_____ Mild
_____ Moderate
_____ Marked
Method (choose what was used for evaluation)
• Correlation was made with a gross photograph of tumor cut surface: Yes _____ No _____
• Evaluation was aided by use of tumor mapping to match a gross photograph to histologic sections: Yes _____ No _____
• Evaluation was aided by radiologic pathologic correlation: Yes _____ No _____
Treatment effect in lymph node metastases
• Total number of lymph node stations examined: _____
• Total number of lymph nodes examined: _____
• No carcinoma present: _____
• Total number of lymph nodes with metastatic carcinoma: _____
• Lymph node stations involved by tumor with treatment-related changes: _____
• Lymph node stations with treatment-related changes without viable tumor: _____
• Largest tumor focus: mm at station number: _____
• Extracapsular extension present: _____
• No extracapsular extension (comment): __________________________________________________________________
Comments: ___________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________

3. IASLC Multidisciplinary Recommendations
for Pathologic Assessment of Lung Cancer
Specimens Following Neoadjuvant Therapy1
Full abbreviations, accreditation, and disclosure information available at
PeerView.com/GZR40
Histologic Components of the Tumor Bed
(A) Schematic image showing how percentage compositions are assigned. The tumor bed is divided into viable tumor area,
necrosis, and stroma. Stroma includes inflammation and fibrosis. (B) A representative hematoxylin-and-eosin stained slide image
(left) and a corresponding color illustration of the distribution of the components (right). The blue, red, and green areas represent
viable tumor, necrosis, and stroma, respectively.
Tumor bed = X + Y + Z = 100%
Viable tumor (X%)
Necrosis (Y%)
Stroma (Z%)
 Viable tumor = 50%
 Necrosis = 40%
 Stroma = 10%
A
B
Tumor bed

4. IASLC Multidisciplinary Recommendations
for Pathologic Assessment of Lung Cancer
Specimens Following Neoadjuvant Therapy1
Full abbreviations, accreditation, and disclosure information available at
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Recommendation 6
Definition of major pathologic response (MPR)
MPR is defined as the reduction of viable tumor to the amount beneath an established clinically significant cutoff based
on prior evidence according to the individual histologic type of lung cancer and a specific therapy.
The historical definition of MPR for all histologic types of lung cancer is ≤10% of viable tumor with no viable tumor
required for pathologic complete response (pCR). MPR is calculated as the estimated size of viable tumor divided by
the size of the tumor bed. For the moment, this is the cutoff being used in multiple active clinical trials. However, recent
data suggests the MPR in the conventional chemotherapy setting may differ according to histologic type: ie,
adenocarcinoma versus squamous cell carcinoma.
If after review of histologic sections, the percentage of viable tumor is near the cutoff for MPR, additional histologic
sections should be submitted. The pathology report should record the total number of blocks of tumor bed that were
examined even if the blocks did not consist entirely of tumor bed but also included some uninvolved lung.
For colloid adenocarcinomas, where tumor cells are only focal, the mucin pools should be included in the percentage
of viable tumor. However, if there are only areas of extracellular mucin without any apparent viable tumor cells within
the mucin, we suggest regarding this as stroma. Further study is needed to address this point.
MPR can also be classified for the lung primary in the setting where the lung primary shows little or no viable tumor,
but lymph nodes show viable metastatic carcinoma (ypT0, N1, 2 or 3). However, the prognostic and therapeutic
implications of this clinical setting are not known.
Recommendation 7
Definition of pathologic complete response (pCR)
pCR is defined as the lack of any viable tumor cells on review of H&E slides after complete evaluation of a resected lung
cancer specimen including all sampled regional lymph nodes. Such tumors would be staged as ypT0N0, according to
the 8th edition AJCC and UICC staging systems.
Note
If no tumor is seen in the initial sections and tissue from the tumor bed remains, additional histologic sections should
be made. The number of additional sections should be whatever seems reasonable in the individual setting depending
on the size of the tumor bed and the capacity of the individual pathology laboratory. If the histologic changes in the initial
sections obtained do not show findings that fit for the effects of therapy, the possibility that the wrong area was sampled
should be considered. In such cases the gross specimen may need to be re-evaluated using radiologic pathologic
correlation and if additional lesions are identified, these should be sampled. The pathology report should record the total
number of blocks of tumor bed that were examined even if the entire block did not consist of tumor bed.
The identification of incidental lesions of squamous cell carcinoma in situ, atypical adenomatous hyperplasia,
adenocarcinoma in situ, or minimally invasive adenocarcinoma in the surrounding lung parenchyma that are clearly
separate from the main tumor for which neoadjuvant therapy was administered does not disqualify a case for
classification as MPR or CPR. This proposal is based on clinical judgement, as currently no clinical data exist to
make a specific recommendation.
In the setting of multiple tumors where a second invasive predominant lung carcinoma is present that was regarded
preoperatively to be an intrapulmonary metastasis but determined to be a second synchronous primary after clinical,
radiologic, pathologic, and/or molecular assessment, it is questionable whether the terms MPR or CPR should be used
if the main tumor otherwise meets the above criteria. No data exists currently to address this question.

5. IASLC Multidisciplinary Recommendations
for Pathologic Assessment of Lung Cancer
Specimens Following Neoadjuvant Therapy1
Full abbreviations, accreditation, and disclosure information available at
PeerView.com/GZR40
Recommendation 8
In the absence of more systemic data regarding the evaluation of tumors following immunotherapy and molecular
targeted therapy, the same approach to pathologic assessment of resected lung cancers in the neoadjuvant setting in
evaluating the percentage of viable tumor, necrosis, and stroma should be used, regardless of the type of neoadjuvant
therapy administered whether it was radiation, chemotherapy, targeted therapy, immunotherapy, chemoradiation,
chemoimmunotherapy, or chemotherapy-targeted therapy. There also may be different features that can be addressed
depending on the type of therapy such as immune cell infiltrates in patients who received immunotherapy.
Recommendation 9
In most cases, the lymph nodes are small enough to completely sample, but if there is a very large metastasis or tumor
bed (>2 cm), the lymph node can be bisected and the central slice through the tumor can be submitted in designated
cassettes. This should also be done during grossing of intraoperative frozen sections of lymph nodes. Depending on
individual laboratory resources, more extensive or even complete sampling can also be done. Then, the same approach
can be used for histologic evaluation that is used for the resected lung cancer, reporting percent viable tumor, necrosis,
and stroma. CPR in a lymph node can be recognized if there is a well-defined scar and/or area of tumor necrosis in the
absence of identifiable viable tumor cells.
Recommendation 10
The following recommendations are made for T-factor staging of neoadjuvant lung cancer resection specimens.
Tumor size
If the viable tumor forms a discrete mass where the size can be measured with a ruler either grossly or microscopically
(where it can be measured on a single H&E slide), this is the preferred approach (see figure). However, if the viable
tumor cannot be measured with a ruler because of either grossly indistinct borders, multiple foci interspersed among
necrosis and/or stroma, or it is present on multiple slides, the viable invasive tumor size should be estimated using the
following formula.
Viable invasive tumor size (cm) = tumor bed size x percentage of viable invasive tumor
Estimating invasive size by adjusting for lepidic component
In tumors that have a component of lepidic growth, tumor size estimation should use the principles introduced in the 8th
Edition TNM classification that record both size and invasive sizes, but only use the invasive size for T-factor
determination. Thus, in the neoadjuvant setting, viable tumor–size estimation for such cases may need two adjustments:
one for the invasive size excluding the lepidic component and a second for the percentage of viable tumor, as outlined
above. However, the clinical implications of this adjustment for the lepidic component are not known in the neoadjuvant
setting.
T3: Multiple tumors considered to represent intrapulmonary metastases
If there is more than one tumor within a lobe, the pathologic response or percentage of viable tumor should be reported
for each tumor, unless the number of intrapulmonary metastases are too numerous to count.
Recommendation 11
Ongoing neoadjuvant studies with targeted therapies and immunotherapies in resectable NSCLC represent a unique
source of information, and the International Association for the Study of Lung Cancer strongly recommends and promotes
the design and implementation of an international database to collect uniformly clinical and pathologic information with
the ultimate goal of fostering collaboration and facilitating the identification of surrogate end points of long-term survival.
1. Travis WD et al. J Thorac Oncol. 2020;15:709-740.

6. Pan-Tumor Pathologic Scoring of Response
to Neoadjuvant Immunotherapy
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Need and Rationale
• Immune checkpoint inhibitor (ICI) therapy is rapidly transitioning from advanced- to early-stage
cancers, with several new FDA approvals in the neoadjuvant setting and many active neoadjuvant
ICI clinical trials underway, creating a need for a standardized, universal scoring system for
pathologic response that encompasses features characteristic of immunotherapy and spans
different tumor types
The definitive surgical resection specimen of a treated tumor provides a unique window at an
early timepoint to assess treatment effect, and evidence is accumulating in multiple tumor types
that percentage of residual viable tumor (% RVT) calculated on H&E slides in surgical pathology
specimens can be used as a surrogate marker of long-term survival
Long-term patient outcomes can be predicted in weeks to months
when the definitive surgical pathology specimen is received
Pathologic findings can help guide further therapy decisions
Terms and Definitions1
% RVT = percentage of residual viable tumor
assessed on post-treatment specimen
Viable tumor = surface area of viable tumor
after therapy
Tumor bed = surface area of tumor before
therapy
• pCR = pathologic complete response,
0% residual viable tumor
• MPR = major pathologic response,
≤10% residual viable tumor
• pPR = partial pathologic response,
>10% and ≤50% residual viable tumora
Commonly Studied Thresholds
of Pathologic Response
• The surface area of the tumor bed is
determined using features that are
common across tissues and tumor types
Immune-Related Pathologic
Response Criteria (irPRC)
Adjuvant immunotherapy
Neoadjuvant immunotherapy
Specimen analyzed by pathologists
Healthy cell
T cell Tumor cell Artery Immunotherapy
a
Preliminary definition used in melanoma (not for all tumor types).

7. Pan-Tumor Pathologic Scoring of Response
to Neoadjuvant Immunotherapy
Full abbreviations, accreditation, and disclosure information available at
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Benefits of a Standardized Pan-Tumor irPRC Scoring System
• Allows for direct comparisons of relative therapeutic efficacy across different tumor types
• Provides a scoring system for tumor types not previously treated in the neoadjuvant setting
• Avoids different scoring systems arising within clinical trials that are subsequently difficult to
implement by pathologists clinically (similar to PD-L1 IHC)
Identifying Features of Tumor Regression and Calculating % RVT2
Proposed reproducible, quantitative irPRC: % RVT is assessed by dividing the total surface
area of RVT (circled in blue below) by the total tumor bed area × 100; the total tumor bed area
(circled in green below) is composed of the regression bed area + RVT area + areas of necrosis
% RVT =
Total tumor bed area
Total area involved by viable tumor
× 100
Recognition of regression influences the score: patterns of immune-mediated regression
Pan-tumor irPRC leverages the
pathologist’s ability to distinguish
between intratumoral stroma
and regressed tumor
Plasma cells
Cholesterol clefts
Foamy
macrophages
Neovascularization
Proliferative fibrosis
Tumor-infiltrating
lymphocytes
Tertiary lymphoid structure
Granulomas

8. Pan-Tumor Pathologic Scoring of Response
to Neoadjuvant Immunotherapy
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IASLC vs Pan-Tumor irPRC: Common Ground2-4
IASLC vs Pan-Tumor irPRC: Key Differences2-4
IASLC and Pan-Tumor irPRC
Grossing
• Submit complete cross section or entire tumor, including tumor
interface with adjacent normal lung
• Photo with block mapping can be helpful
RVT reporting recommendations • If RVT ≥10%, report in 10% increments
Tumor bed definition
• Total area originally involved by tumor
• Excludes other diagnosable processes such as pneumonia,
downstream obstructive changes, and other associated
nonspecific “reactive” processes
Lymph nodes
• Recommend quantitative scoring of lymph nodes using the same
approach as in the primary tumor
IASLC irPRC
Tumor bed components
(= 100%)
% tumor + % necrosis + % stroma
% tumor (including intratumoral stroma
that is not regression)
+ % necrosis + % regression
% tumor Area of tumor epithelium only
Area of tumor epithelium
and intratumoral stroma
% stroma
Area of inflammation and fibrosis
(including intratumoral stroma)
N/A
% regression/regression
bed
N/A
Region(s) of the radiographically and
grossly identifiable “tumor mass” that
have been replaced by a wound healing
response (proliferative fibrosis with
neovascularization) and evidence
of immune activation and tumor cell death
Development
and validation
Development: neoadjuvant
chemotherapy
Validation: ongoing
Development: neoadjuvant anti–PD-1
Validation: chemo alone and chemo + IO
1. Krishnamoorthy M et al. J Natl Cancer Inst. 2021;113:823-832. 2. Cottrell TR et al. Ann Oncol. 2018;29:1853-1860. 3. Travis WD et al. J Thorac Oncol. 2020;15:709-740.
4. Analysis provided courtesy of Janis Taube, MD, MSc.

9. Principles and Guideline Recommendations
for PD-L1 Assessment
Full abbreviations, accreditation, and disclosure information available at PeerView.com/GZR40
a
Images courtesy of Sanjay Mukhopadhyay, MD. b
Images courtesy of Kurt A. Schalper, MD, PhD.
Principles of PD-L1 Assessment by IHC
• Use a validated IHC assay and proper controls
(eg, cell lines, tonsil, placenta)
• Sample should meet preanalytical requirements
(eg, fixation, thin section, storage)
• Consider tumor/assay-specific differences
(eg, pattern, scoring system, cutpoints)
• PD-L1 detected in tumor and stromal cells
(eg, >100 cells, only tumor score reliable)
• Membranous staining in tumor cells; can be
cytoplasmic in immune cells (incomplete)
• The intensity of staining is not considered in the
scoring (eg, any intensity counts)
• Exclude areas of dysplasia, noninvasive
disease, necrosis, and nontumor tissue
• PD-L1 staining can be heterogeneous
(eg, integrate scores)
Tumor and Immune/Stromal Cells
Can Express PD-L1a
Non–Small Cell Lung Carcinoma
Gastric Adenocarcinoma
PD-L1 Staining Can Be Heterogeneousb

10. Principles and Guideline Recommendations
for PD-L1 Assessment
Full abbreviations, accreditation, and disclosure information available at PeerView.com/GZR40
1. https://www.cap.org/protocols-and-guidelines/upcoming-cap-guidelines/pd-l1-testing-of-patients-with-lung-cancer-for-immunooncology-therapies.
Draft Recommendation Statements
1. In patients with advanced NSCLC, clinicians should use a validated PD-L1 IHC expression assay, in conjunction
with other targetable genomic biomarker assays where appropriate, to optimize selection for treatment with
immune checkpoint inhibitors
2. Clinicians should test for PD-L1 expression using the best available specimen (note: laboratories should ensure
appropriate validation has been performed on all specimen types and fixatives)
3. When feasible, laboratorians should use clinically validated PD-L1 IHC assays as intended
4. Laboratories that choose to use laboratory-developed tests for PD-L1 expression should validate according to the
requirements of their accrediting body
5. Laboratorians should report PD-L1 IHC results using a percent expression score
6. Clinicians should not use TMB alone to select patients with advanced NSCLC for immune checkpoint inhibitors
based on insufficient evidence in this population
CAP Guidelines: Testing of Patients With Lung Cancer for Immunotherapies1

11. MSI/MMR in Immunotherapy Biomarker Testing
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PCR + Capillary Electrophoresis
Immunohistochemistry
MLH1 MSH2
MSH6 PMS2
• No specific DNA requirement
• Only tumor biopsy/tissue
• 4 x 5-micron sections
• Any tumor cell content
• Widely available
• Sensitivity: 85%
• >20- to 30-ng DNA
• Tumor and nontumor sample
• 4 to 10 x 5-micron sections
• >25% to 30% tumor cells
• Not widely available
• Sensitivity: 93%
How to Test for MSI or dMMR: Immunohistochemistry and PCR + Capillary Electrophoresisa
MSI IHC Requirements and Performance PCR Test Requirements/Performance
a
Images courtesy of Kurt A. Schalper, MD, PhD.

12. MSI/MMR in Immunotherapy Biomarker Testing
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How to Test for MSI or dMMR: Next-Generation Sequencing1
• Tumor only required
• Obtained as part of some NGS panels that may already be
performed as part of standard of care (not a separate test)
• May have improved performance for NGS detection for certain
tumor types (non-CRC)
• Sensitivity: >95%
MSI NGS Requirements/Performance

13. MSI/MMR in Immunotherapy Biomarker Testing
Full abbreviations, accreditation, and disclosure information available at PeerView.com/GZR40
1. Papke DJ et al. Mod Pathol. 2018;31:1882-1890. 2. https://documents.cap.org/documents/mmr-msi-summary-recommendations.pdf. 3. Bartley AN et al. Arch Pathol Lab Med. 2022;146:1194-1210. 4. Vikas P et al. J Clin Oncol. 2023;JCO2202462.
CAP Guidelines: MMR and MSI Testing for Immune Checkpoint Inhibitor Therapy2-4
Strength of
Recommendation
Guideline Statement
Strong
1. For patients with CRC being considered for immune checkpoint inhibitor therapy, pathologists should use
MMR-IHC and/or MSI by PCR for the detection of DNA MMR defects. Although MMR-IHC or MSI by PCR
is preferred, pathologists may use a validated MSI by NGS assay for the detection of DNA MMR defects.
Note: MSI by NGS assay must be validated against MMR-IHC or MSI by PCR and must show equivalency.
Strong
2. For patients with gastroesophageal and small bowel cancer being considered for immune checkpoint
inhibitor therapy, pathologists should use MMR-IHC and/or MSI by PCR over MSI by NGS for the
detection of DNA MMR defects.
Note: This recommendation does not include esophageal squamous cell carcinoma.
Strong
3. For patients with endometrial cancer being considered for immune checkpoint inhibitor therapy,
pathologists should use MMR-IHC over MSI by PCR or NGS for the detection of DNA MMR defects.
Conditional
4. For patients with cancer types other than CRC, GEA, small bowel, and endometrial being considered
for immune checkpoint inhibitor therapy, pathologists should test for DNA MMR, although the optimal
approach for the detection of MMR defects has not been established.
Note: Assays must be adequately validated for the specific cancer type being tested with careful
consideration of performance characteristics of MMR-IHC and MSI by NGS or PCR for the detection
of DNA MMR defects.
Strong
4. For all cancer patients being considered for immune checkpoint inhibitor therapy based upon defective
MMR, pathologists should not use TMB as a surrogate for the detection of DNA MMR defects. If a tumor
is identified as TMB high, pathologists may perform IHC and/or MSI by PCR to determine if high TMB is
secondary to MMR deficiency.
Strong
5. For cancer patients being considered for immune checkpoint inhibitor therapy, if an MMR deficiency
consistent with Lynch syndrome is identified in the tumor, pathologists should communicate this finding
with the treating physician.