Faculty Bibliography

Assessment of the immune response to tumors is growing in importance as the prognostic implications of this response are increasingly recognized, and as immunotherapies are evaluated and implemented in different tumor types. However, many different approaches can be used to assess and describe the immune response, which limits efforts at implementation as a routine clinical biomarker. In part 1 of this review, we have proposed a standardized methodology to assess tumor-infiltrating lymphocytes (TILs) in solid tumors, based on the International Immuno-Oncology Biomarkers Working Group guidelines for invasive breast carcinoma. In part 2 of this review, we discuss the available evidence for the prognostic and predictive value of TILs in common solid tumors, including carcinomas of the lung, gastrointestinal tract, genitourinary system, gynecologic system, and head and neck, as well as primary brain tumors, mesothelioma and melanoma. The particularities and different emphases in TIL assessment in different tumor types are discussed. The standardized methodology we propose can be adapted to different tumor types and may be used as a standard against which other approaches can be compared. Standardization of TIL assessment will help clinicians, researchers and pathologists to conclusively evaluate the utility of this simple biomarker in the current era of immunotherapy.

This session will focus on some new definitions and concepts in the recently published 2015 WHO classification of lung tumors1, some of which were showcased in the 2011 IASLC/ATS/ERS lung adenocarcinoma classification2, while others are introduced for the first time. We will focus on resected lung adenocarcinoma as well resected squamous cell carcinoma, large cell carcinoma and the neuroendocrine tumor spectrum. Adenocarcinoma: In the 2015 WHO classification, the definition of adenocarcinoma has been expanded from a malignant epithelial tumor with glandular differentiation or mucin production to include tumors that also express pneumocyte immunomarkers (e.g. TTF1, Napsin A). This means that undifferentiated carcinomas formerly classified as large cell carcinoma that express pneumocyte immunomarkers, like undifferentiated carcinomas that show mucin expression, are now included in the solid adenocarcinoma category. Invasive adenocarcinomas account for >70% of all surgically resected cases and consist of a complex admixture of histologic subtypes. In an effort to represent this morphologic complexity, comprehensive histologic subtyping was introduced in the 2011 IASLC/ATS/ERS classification. A number of recent studies have demonstrated the utility of comprehensive histologic subtyping in identifying prognostically significant groups of tumors. Studies published both before and after the 2011 IASLC/ATS/ERS classification have highlighted the importance of the secondary patterns in addition to the predominant pattern in resected lung adenocarcinoma. Comprehensive histologic subtyping, its pitfalls and the emerging significance of secondary patterns in tumor recurrence and prognosis will be discussed further in this session. Grading: There is no well-established, internationally accepted grading system in resected lung adenocarcinoma. A simple grading system based on predominant histologic subtype has been proposed due to the prognostic significance of predominant histologic subtype. Other suggested grading schemes include different combinations of mitotic count, second predominant pattern and nuclear features with predominant histologic subtype. The emerging concept of an objective grading system for pulmonary adenocarcinomas will be briefly explored in this session. Another newly introduced concept in the 2015 WHO classification is that of tumor spread through alveolar spaces (STAS) which may occur with micropapillary clusters, solid nests or single cells. STAS was found to be associated with an increased recurrence rate in patients with stage I adenocarcinomas <2cm who underwent sublobar resections.3 Tumor Size and Staging: A recent study confirmed that in resected non-mucinous adenocarcinoma, the size of the invasive component, excluding the lepidic (equated with in situ) component of the tumor, correlates better with patient outcome than total tumor size.4 This finding has been supported by other studies and is expected to be included in the upcoming 8th edition TNM staging system for the T descriptor for pathologic staging in resected non-mucinous adenocarcinoma.5 Squamous Cell Carcinoma (SQCC): SQCC is the second most prevalent non-small cell lung cancer (NSCLC), behind adenocarcinoma. Contrary to the latter where most changes in nomenclature, diagnosis and molecular pathology have occurred, SQCC has a strong association to smoking and remains a challenge for oncologists with few therapeutic advances. To reduce the risk of over diagnosing SQCC, the definition of SQCC became stricter in the 2015 WHO classification. For the diagnosis of this entity it is necessary to have evidence of keratinization and intercellular bridges. For non-keratinizing SQCC it is necessary to demonstrate evidence of squamous differentiation by immunohistochemical (IHC) stain (diffuse positivity for p40 or p63 and absence of adenocarcinoma markers such as TTF-1 and napsin-A). Non-keratinizing SQCC shares a solid pattern of growth with adenocarcinoma; in addition, solid type adenocarcinomas can have squamoid features such as glassy and abundant cytoplasm that can mimic SQCC6, therefore it is recommended the use of IHC for any NSCLC with solid pattern of growth. Presence or absence of mucin is not a criterion for diagnosis of SQCC. Similar to adenocarcinoma, there is no grading system for SQCC. There is evidence that tumor budding is associated with worse prognosis.7 Basaloid carcinoma is now classified in the same group of SQCC and no longer part of large cell carcinoma. In contrast, Lymphoepithelioma-like carcinoma of the lung that share IHC profile with squamous cell carcinoma is grouped in the category of other undifferentiated tumors that also include NUT carcinoma. Large Cell Carcinoma: This remains a separate category; however, the diagnosis of this entity is greatly reduced. Large cell carcinoma is an undifferentiated carcinoma (positive for cytokeratin markers), which lacks evidence of differentiation by morphology and lineage specific immunohistochemical profile (TTF-1/Napsin-A and p40 negative). This classification is supported by molecular profile.8 High Grade Neuroendocrine Carcinomas: This tumor category remains largely the same from previous classification with the exception that Large Cell Neuroendocrine Carcinoma (LCNC) is now grouped with neuroendocrine tumors. It is no longer part of a Large Cell Carcinoma category. Recent studies have suggested that LCNEC is a heterogeneous group ranging in the spectrum from NSCLC-like to small cell carcinoma-like tumors.9 LCNEC that resemble NSCLC have higher incidence of KRAS mutations, whereas those morphologically closer to small cell carcinoma have higher incidence of RB mutation. The significance of these findings for tumor classification and especially for therapeutic options are still unknown as more studies need to be done. There have been several studies on the genetic and epigenetic profile of small cell carcinoma that could lead to new therapeutic options.10 However, the diagnosis and classification of this tumor remains the same. Carcinoid Tumors: Typical and atypical carcinoid tumors maintained the same morphological criteria for diagnosis and classification. Recent molecular studies have showed however that these tumors have distinct molecular profiles from the high grade relatives (LCNC and small cell carcinoma).10

Assessment of tumor-infiltrating lymphocytes (TILs) in histopathologic specimens can provide important prognostic information in diverse solid tumor types, and may also be of value in predicting response to treatments. However, implementation as a routine clinical biomarker has not yet been achieved. As successful use of immune checkpoint inhibitors and other forms of immunotherapy become a clinical reality, the need for widely applicable, accessible, and reliable immunooncology biomarkers is clear. In part 1 of this review we briefly discuss the host immune response to tumors and different approaches to TIL assessment. We propose a standardized methodology to assess TILs in solid tumors on hematoxylin and eosin sections, in both primary and metastatic settings, based on the International Immuno-Oncology Biomarker Working Group guidelines for TIL assessment in invasive breast carcinoma. A review of the literature regarding the value of TIL assessment in different solid tumor types follows in part 2. The method we propose is reproducible, affordable, easily applied, and has demonstrated prognostic and predictive significance in invasive breast carcinoma. This standardized methodology may be used as a reference against which other methods are compared, and should be evaluated for clinical validity and utility. Standardization of TIL assessment will help to improve consistency and reproducibility in this field, enrich both the quality and quantity of comparable evidence, and help to thoroughly evaluate the utility of TILs assessment in this era of immunotherapy.

CONTEXT: - The diagnosis and grading of acute cellular and antibody-mediated rejection (AMR) in lung allograft biopsies is important because rejection can lead to acute graft dysfunction and/or failure and may contribute to chronic graft failure. While acute cellular rejection is well defined histologically, no reproducible specific features of AMR are currently identified. Therefore, a combination of clinical features, serology, histopathology, and immunologic findings is suggested for the diagnosis of AMR. OBJECTIVE: - To describe the perspective of members of the Pulmonary Pathology Society (PPS) on the workup of lung allograft transbronchial biopsy and the diagnosis of acute cellular rejection and AMR in lung transplant. DATA SOURCES: - Reports by the International Society for Heart and Lung Transplantation (ISHLT), experience of members of PPS who routinely review lung allograft biopsies, and search of literature database (PubMed). CONCLUSIONS: - Acute cellular rejection should be assessed and graded according to the 2007 working formulation of the ISHLT. As currently no specific features are known for AMR in lung allografts, the triple test (clinical allograft dysfunction, donor-specific antibodies, pathologic findings) should be used for its diagnosis. C4d staining might be performed when morphologic, clinical, and/or serologic features suggestive of AMR are identified.

INTRODUCTION: The current WHO classification of lung cancer states that a diagnosis of SCLC can be reliably made on routine histological and cytological grounds but immunohistochemistry (IHC) may be required, particularly (1) in cases in which histologic features are equivocal and (2) in cases in which the pathologist wants to increase confidence in diagnosis. However, reproducibility studies based on hematoxylin and eosin-stained slides alone for SCLC versus large cell neuroendocrine carcinoma (LCNEC) have shown pairwise kappa scores ranging from 0.35 to 0.81. This study examines whether judicious use of IHC improves diagnostic reproducibility for SCLC. METHODS: Nineteen lung pathologists studied interactive digital images of 79 tumors, predominantly neuroendocrine lung tumors. Images of resection and biopsy specimens were used to make diagnoses solely on the basis of morphologic features (level 1), morphologic features along with requested IHC staining results (level 2), and all available IHC staining results (level 3). RESULTS: For the 19 pathologists reading all 79 cases, the rate of agreement for level 1 was 64.7%, and it increased to 73.2% and 77.5% in levels 2 and 3, respectively. With IHC, kappa scores for four tumor categories (SCLC, LCNEC, carcinoid tumors, and other) increased in resection samples from 0.43 to 0.60 and in biopsy specimens from 0.43 to 0.64. CONCLUSIONS: Diagnosis using hematoxylin and eosin staining alone showeds moderate agreement among pathologists in tumors with neuroendocrine morphology, but agreement improved to good in most cases with the judicious use of IHC, especially in the diagnosis of SCLC. An approach for IHC in the differential diagnosis of SCLC is provided.