American Registry of Pathology Expert Opinions: Evaluation of poorly differentiated malignant neoplasms on limited samples - Gastrointestinal mucosal biopsies

Gastrointestinal Stromal Tumors: Variants and Some Pitfalls That They Create

The diagnosis of gastrointestinal stromal tumors (GISTs) is generally straightforward using a combination of histologic evaluation and pertinent immunohistochemical staining with CD117/kit and DOG-1 (discovered on GIST) antibodies. However, this tumor can be challenging in cases with an unusual morphology, in limited biopsies, for those in uncommon sites, post-treatment, and when other neoplasms express CD117/kit and DOG-1, thereby mimicking GIST. Finding epithelioid GISTs in the stomach in younger patients should prompt testing for succinate dehydrogenase (SHD)-deficiency using immunohistochemical staining for subunit B (SDHB). However, SDH-deficient GISTs can also arise in older patients, or as part of the Carney triad or Carney-Stratakis syndrome. GISTs with PDGFRA mutations can also prove difficult if they lack kit expression. It is also important to consider morphologic and immunophenotypic changes associated with treatment, including the potential absence of kit expression, particularly in GISTs that have metastasized. Therefore, obtaining clinical information regarding prior therapy with a tyrosine kinase inhibitor (TKI) is crucial.

Current Approach to Undifferentiated Neoplasms, With Focus on New Developments and Novel Immunohistochemical Stains

CONTEXT.—

Workup of the poorly differentiated or undifferentiated tumor remains a significant and challenging entity in the practice of anatomic pathology. Particularly in the setting of small biopsies and limited material, these cases demand a balanced approach that considers the patient's clinical and radiologic presentation, a basic assessment of tumor morphology, a reasonably broad immunohistochemical panel, and diligent preservation of tissue for prognostic and therapeutic studies.

OBJECTIVE.—

To illustrate some of the new and emerging immunohistochemical markers in the evaluation of tumors with undifferentiated or poorly differentiated morphology, with a focus on the workup in limited tissue samples to raise awareness of the issues involved with the pathologic workup in these challenging tumors.

DATA SOURCES.—

A literature review of new ancillary studies that can be applied to cytologic specimens was performed.

CONCLUSIONS.—

Knowledge of the patient's history and communication with the patient's clinical team is essential in formulating a differential diagnosis that can appropriately limit the differential diagnosis based on morphology, especially in small specimens. This information, in conjunction with classifying the tumor morphology (eg, epithelioid, spindled, neuroendocrine, basaloid/biphasic, mixed) gives a logical approach to choosing an initial immunohistochemical panel. Fortunately, immunohistochemistry is evolving quickly in the wake of groundbreaking molecular studies to develop new and better markers to further classify these difficult tumors beyond where we traditionally have been able to go.

Some Morphology Frontiers of Dysplasia in the Tubular Gastrointestinal Tract: The Rodger C. Haggitt Memorial Lecture

This review, based on the content of the 2020 US Gastrointestinal Pathology Society's Rodger Haggitt Lecture, concerns an array of tubular gastrointestinal tract dysplastic or possible "predysplastic lesions" with an almost purely morphologic focus based on our collaborative efforts over the past few years. These processes include esophageal epidermoid metaplasia, Barrett esophagus-associated dysplasia, polypoid gastric dysplastic lesions, small intestinal dysplasia, and the ability of metastases to mimic it, the controversial "serrated epithelial change" encountered in the setting of long-standing ulcerative and Crohn colitis, and recently described anal columnar human papilloma virus-associated neoplasms.

Variations of P40 and P63 Immunostains in Different Grades of Esophageal Squamous Cell Carcinoma: A Potential Diagnostic Pitfall

The distinction of esophageal squamous cell carcinoma (SCC) from adenocarcinoma (adenoCA) using targeted therapies has become critical for small biopsies. In the United States, esophageal SCC is relatively uncommon compared with AdenoCA, with only few detailed immunohistochemical (IHC) studies on esophageal SCC. We characterized p40 and p63 IHC across various grades of squamous differentiation in esophageal SCC and compared their sensitivities between esophageal SCC and adenoCA. Twenty-eight esophageal SCC and 26 esophageal adenoCA (control group) samples were stained for p40, p63, and CK5/6. All hematoxylin-and-eosin-stained SCC slides were reviewed. Tumors were graded according to the World Health Organization classification: well, moderately, or poorly differentiated (WD, MD, and PD, respectively). Considering morphological heterogeneity, individual differentiation components within the same tumor were scored separately (0% to 100%) according to the proportion of immunoreactive cells and marked as positive (≥5%) or negative (<5%). Among 28 esophageal SCC, 15 had mixed intratumoral differentiation. There were 16 WD, 19 MD, and 14 PD components. P40 immunoreactivity was significantly lower in WD than in MD or PD components (P<0.001), P63 immunoreactivity patterns were similar (P<0.001), while CK5/6 showed no differences (P>0.05). The sensitivities for SCC components were 98% (P40), 100% (P63), and 100% (CK5/6), while those for esophageal AdenoCA were significantly lower: 4% (P40), 4% (P63), and 8% (CK5/6). P40 and P63 were sensitive and specific for routine esophageal SCC diagnosis. However, their immunostaining was significantly lower in WD SCC than in higher grade tumors. IHC results for small biopsy specimens should be interpreted carefully, particularly in WD components.

Signet Ring Cell Features are Associated with Poor Response to Neoadjuvant Treatment and Dismal Survival in Patients with High-Grade Esophageal Adenocarcinoma

BACKGROUND

While the prognosis of patients with locoregional esophageal adenocarcinoma (EAC) has improved in the neoadjuvant treatment (NAT) era, high-grade histology (G3) is still associated with a limited treatment response. We sought to investigate oncologic outcomes in patients after esophagectomy for G3 EAC and to identify predictors of poor survival among these patients.

METHODS

Patients with EAC who underwent resection with curative intent in 2011-2018 were divided by histologic grade (G3, G1/2) and compared for overall survival (OS). Cox regression was performed to analyze the response to NAT and the predictive role of signet ring cell (SRC) features.

RESULTS

The cohort included 163 patients, 94 (57.7%) with G3 histology. NAT was administered to 69 (73.4%) patients. Following resection, OS in the G3 EAC group was 30 months (95% confidence interval [CI] 23.9-36.1). On univariate analysis, G3 disease (p = 0.050) and SRC features (p = 0.019) predicted low OS. Median survival in the G3 EAC group was worse in patients with SRC histology (18 months, 95% CI 8.6-27.4) than those without (30 months, 95% CI 23.8-36.1; p = 0.041). No patients with SRC histology were alive at 5 years of follow-up. Among all patients administered NAT, 88.2% of those with SRC showed minimal or no pathologic response and only 27.8% were downstaged.

CONCLUSIONS

High-grade histology was found in most patients with EAC and predicted poor survival and treatment response. SRC features in patients with G3 disease were associated with lower OS. The benefit of NAT for G3 EAC in patients with SRC histology appears limited.

Diagnostic Utility of INSM1 in Medullary Thyroid Carcinoma

Insulinoma-associated protein 1 (INSM1) is shown to be an excellent marker for neuroendocrine differentiation. However, the diagnostic utility of INSM1 in medullary thyroid carcinoma (MTC) has not yet been extensively investigated. INSM1 staining was performed on 21 MTCs, 7 MTC mimickers (including 3 papillary carcinomas, 2 poorly differentiated carcinomas, 1 follicular adenoma, and 1 nodular plasma cell hyperplasia), and 3 cases of C-cell hyperplasia. INSM1 staining of these cases was compared with the traditional MTC markers including calcitonin (CT), monoclonal carcinoembryonic antigen (mCEA), chromogranin A (CgA), and synaptophysin (Syn). The H-score was generated using the QuPath program, an open-source image analysis software. All 21 MTC cases and 3 C-cell hyperplasia cases were positive for all markers. The MTC mimickers were entirely negative for INSM1. INSM1 and Syn displayed, more consistently, high expression with minimal variability than CgA that showed a wide range of expression with significant variability. mCEA and CT exhibited mostly a high expression with some variability. Being a nuclear stain, interpretation was easier with INSM1 compared to other cytoplasmic markers. INSM1 is an excellent marker for neuroendocrine differentiation, entirely applicable in the diagnosis of MTC and C-cell hyperplasia with high sensitivity and specificity. In comparison with the traditional MTC markers, INSM1 is unique in the crisp nuclear staining pattern with a consistent, diffuse, and strong expression. INSM1 can be potentially combined with CT or mCEA as a dual stain, especially when the lesional tissue is limited for a panel of immunostains.

Highly proliferative anal neuroendocrine carcinoma: molecular and clinical features of a rare, recurrent case in complete remission

BACKGROUND

Poorly differentiated anal neuroendocrine carcinomas (ANECs) are rare lesions with poor prognosis, and the molecular etiology is only partially understood.

CASE PRESENTATION

At our institution, we have treated and followed a patient with such a rare ANEC. He had primarily surgery followed by three rounds of repeated surgery for loco-regional recurrences. He also received three different combinations of chemotherapy and external beam radiation. At last follow-up 13 years since the primary diagnosis, the patient had been in complete remission for nine years. The patient's medical files were re-examined, including laboratory, radiology and clinical examinations. Histopathology was re-assessed, and expanded immunohistochemistry was performed from tissue specimens from the four surgical procedures. In addition, the molecular genetic status was evaluated through next-generation sequencing. The initial tumor was consistent with a 59 mm small cell neuroendocrine cancer with a Ki-67 index of 80%. Regional lymph node metastases were evident, and immunohistochemistry supported a neuroendocrine origin. A PCR screening detected human papilloma virus type 45 DNA (high-risk subtype), and focused next-generation sequencing found a missense mutation in the Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha (PIK3CA) gene. In tissues representing subsequent recurrences, the Chromogranin A expression was lost, and the Ki-67 index increased to 90%.

CONCLUSIONS

For the first time, we report the detection of HPV45 in a case of ANEC. To our belief, PIK3CA mutations have also not been previously demonstrated in this tumor entity. In highly malignant ANECs, cure can in rare cases be achieved. Although speculative, expression of HPV45 and/or the PIK3CA mutation may have contributed to the favorable outcome.