ALK Immunohistochemistry and Molecular Analysis in Uterine Inflammatory Myofibroblastic Tumor: Proceedings of the ISGyP Companion Society Session at the 2020 USCAP Annual Meeting

Advances in uterine inflammatory myofibroblastic tumours: Diagnostic challenges and risk stratification

The current understanding of inflammatory myofibroblastic tumours (IMTs) of the gynaecological tract has recently been enhanced by their increased recognition. This increase is largely due to greater accessibility to RNA-based molecular assays used to identify their defining ALK rearrangements. This review summarises the clinical characteristics, morphological spectrum, immunohistochemical profile and molecular underpinnings of uterine IMT. Additionally, this review discusses practical diagnostic considerations including overlap between uterine IMT and smooth muscle tumours as well as pregnancy-associated uterine IMT. Finally, we highlight recent literature demonstrating the potential for aggressive behaviour in uterine IMT, including a novel risk stratification model for identifying high-risk IMT.

Uterine Leiomyoma-Like Inflammatory Myofibroblastic Tumor Without Myxoid Matrix or Inflammatory Cell Infiltration: A Case Report of a Potential Diagnostic Pitfall

Inflammatory myofibroblastic tumors (IMTs) of the uterus are relatively rare. Although most IMTs exhibit indolent biological behaviors, local recurrence, and metastasis may occur. Such patients may benefit from targeted therapy; therefore, precise diagnosis is essential for clinical follow up and treatment. Here, we describe a 33-year-old woman with a uterine mass that was detected 4 years previously during pregnancy. The morphology of the tumor resembled that of a uterine leiomyoma, lacking myxoid matrix, and inflammation. Following immunohistochemical and molecular analyses, the tumor was definitively identified as a uterine IMT based on its morphological features. The uterine IMT described in this case had a rare morphology, which can be easily misdiagnosed based on histology alone. Hence, understanding the morphological changes of IMTs in greater detail is imperative to facilitate their accurate diagnosis.

The "Other" Uterine Mesenchymal Neoplasms: Recent Developments and Emerging Entities

Uterine mesenchymal neoplasms are a challenging group of tumors that often show overlapping morphologic features and immunohistochemical profiles. The increasing use of molecular testing in these tumors has enabled a better appreciation of their pathobiology, resulting in a wave of emerging neoplasms and improved characterization of ones previously considered exceptionally rare. Identification of specific molecular alterations has permitted targeted therapy options in tumors that were typically unresponsive to conventional therapies, as well as recognition that a subset can have a hereditary basis. This review will discuss the more "common" of the uncommon uterine mesenchymal neoplasms, including inflammatory myofibroblastic tumor, perivascular epithelioid cell tumor, uterine tumor resembling ovarian sex cord tumor, and embryonal rhabdomyosarcoma. This will be followed by an overview of emerging entities, including NTRK-rearranged uterine sarcoma, SMARCA4-deficient uterine sarcoma, KAT6B/A::KANSL1 fusion uterine sarcoma, and MEIS1::NCOA2/1 fusion sarcoma.

Leiomyoma-like Morphology in Metastatic Uterine Inflammatory Myofibroblastic Tumors

Uterine inflammatory myofibroblastic tumors (IMTs) are rare mesenchymal neoplasms that frequently harbor ALK gene rearrangements and have a low risk of metastasis. We reported 3 of these tumors mimicking the appearance of leiomyoma in their recurrence. These patients were 34, 43, and 45 years old. Two uterine tumors demonstrated classic morphology, with combined myxoid, compact fascicular, and hyalinized patterns and spindled cells with bipolar cytoplasmic processes, moderate atypia, and lymphoplasmacytic inflammatory infiltrates. The third had a "leiomyoma-like" appearance, with fascicles of plump spindled cells and a sparse lymphoplasmacytic infiltrate. ALK immunohistochemistry was positive in all the tumors, and all demonstrated ALK rearrangements using fluorescence in situ hybridization (n = 2) and/or RNA sequencing (n = 2). Two classic IMTs recurred at 3 and 50 months in the lung and abdomen, respectively, and recurrent tumors had a "leiomyoma-like" appearance, with 0 and 1 mitosis per 10 high-power fields, no inflammation in 1, and a sparse lymphocytic infiltrate in the other. ALK was positive in both tumors; 1 with available tissue showed an IGFBP5::ALK fusion using RNA sequencing. The third patient, who had a "leiomyoma-like" uterine tumor, experienced multiple recurrences, first in the abdomen at 100 months showing a similar appearance. Subsequent recurrence at 105 months showed transmural invasion of the sigmoid colon and a similar microscopic appearance but with the addition of infiltrative borders, moderate cellularity, mild-to-moderate atypia, and 10 mitoses per 10 high-power fields. Both recurrences were positive for ALK, and RNA sequencing revealed the same ACTG2::ALK fusion transcript identified in the primary tumor. The patient was treated with crizotinib, resulting in prolonged clinical remission, with no evidence of disease at 168 months from the initial surgery. Although "leiomyoma-like" uterine IMTs have been recently described, to our knowledge, this is the first report of recurrence of these tumors and the first report of a "leiomyoma-like" appearance in the recurrences of conventional uterine IMTs. A low threshold for performing ALK immunohistochemistry on recurrent uterine tumors can identify patients who may benefit from tyrosine kinase inhibitors.

Uterine Inflammatory Myofibroblastic Tumors: Proposed Risk Stratification Model Using Integrated Clinicopathologic and Molecular Analysis

Inflammatory myofibroblastic tumor (IMT) of the uterus is a rare mesenchymal tumor with largely benign behavior; however, a small subset demonstrate aggressive behavior. While clinicopathologic features have been previously associated with aggressive behavior, these reports are based on small series, and these features are imperfect predictors of clinical behavior. IMTs are most commonly driven by ALK fusions, with additional pathogenic molecular alterations being reported only in rare examples of extrauterine IMTs. In this study, a series of 11 uterine IMTs, 5 of which demonstrated aggressive behavior, were evaluated for clinicopathologic variables and additionally subjected to capture-based next-generation sequencing with or without whole-transcriptome RNA sequencing. In the 6 IMTs without aggressive behavior, ALK fusions were the sole pathogenic alteration. In contrast, all 5 aggressive IMTs harbored pathogenic molecular alterations and numerous copy number changes in addition to ALK fusions, with the majority of the additional alterations present in the primary tumors. We combined our series with cases previously reported in the literature and performed statistical analyses to propose a novel clinicopathologic risk stratification score assigning 1 point each for: age above 45 years, size≥5 cm,≥4 mitotic figures per 10 high-power field, and infiltrative borders. No tumors with 0 points had an aggressive outcome, while 21% of tumors with 1 to 2 points and all tumors with ≥3 points had aggressive outcomes. We propose a 2-step classification model that first uses the clinicopathologic risk stratification score to identify low-risk and high-risk tumors, and recommend molecular testing to further classify intermediate-risk tumors.

Uterine inflammatory myofibroblastic tumor

Inflammatory myofibroblastic tumor (IMT) is recognized as a true neoplasm of unknown etiology, but its pathogenesis is related to abnormalities in the ALK gene. This is an uncommon tumor with a wide anatomic distribution and often constitutes a challenging diagnosis owing to its histological similarities with other tumors. Uterine IMTs are rare and their detailed characteristics should be described based on case reports and small case series. Thus, we performed a comprehensive review of the literature showing that uterine IMTs show a wide range of age at diagnosis (median, 39 years), and a symptomatology similar to that of common leiomyomas, only rarely presenting with inflammatory manifestations. IMTs represent 0.1% of "leiomyomas," an estimate that increases to 10% for pregnant women and to 14% for the smooth muscle tumors of uncertain malignant potential (STUMP) category of tumors, implying that tumors excised during pregnancy, STUMPs, and leiomyosarcomas should be systematically screened with ALK immunohistochemistry, as this is a targetable abnormality. Most reported cases are ALK-positive; the fusion partners vary, but in pregnancy-associated tumors, TIMP3 prevails. Almost 25% of the patients will show an aggressive course, and this is associated with older age, non-pregnancy-associated tumors, larger tumors, infiltrative tumor border, absence of abundant inflammation, atypia, important mitotic activity, and necrosis.

Fertility-preserving management of an inflammatory myofibroblastic tumor: A case report and review of the literature

Molecular diagnostics have broadened the categorization of mesenchymal tumors of the uterus. Knowledge of the increasing heterogeneity of uterine neoplasms is paramount for the gynecologist as the management and prognosis of these neoplasms differ from those of typical leiomyomas. In this case, a 26-year-old nulligravid patient underwent hysteroscopic management for an enlarging submucosal neoplasm of the uterus. She was found to have an inflammatory myofibroblastic tumor (IMT) after ALK (anaplastic lymphoma kinase) immunostaining. Upon review of pathologic characteristics, she was treated expectantly with repeat hysteroscopy 12 months later. Ongoing conservative management will entail serial pelvic imaging. IMTs should be considered in the differential diagnosis of fibroids presenting in young women. Fertility-preserving management in select patients is appropriate after patient counselling.

Case Report: Clinical response to anaplastic lymphoma kinase inhibitor-based targeted therapy in uterine inflammatory myofibroblastic tumor harboring ALK-IGFBP5 fusion

Background

An inflammatory myofibroblastic tumor (IMT) is a mesenchymal tumor with a prevalence ranging from 0.04% to 0.7% worldwide, in which the lung is the most common predilection site, accounting for 33% of cases, followed by the abdomen, pelvis, mesentery, and uterus. Approximately 50% of uterine IMTs present as anaplastic lymphoma kinase (ALK) positive along with ALK gene fusion, which lays a solid foundation for the development of ALK-based target therapy to optimize treatment strategies.

Case presentation

Herein we describe a 57-year-old woman who presented with a slow-growing mass in the uterus for over 10 years and then received surgical resection because of significant progressive enlargement of the mass during follow-up. She was diagnosed with uterine leiomyosarcoma (LMS) with no further interventions until recurrence. We revised the diagnosis to uterine IMT based on diffuse ALK expression, ALK-IGFBP5 gene fusion, and the morphologic features of the tumors by pathology consultation. Based on these, we recommended an ALK tyrosine kinase inhibitor (TKI) treatment, crizotinib (250 mg bid), and she achieved a complete response (CR) with at least 18 months of progression-free survival (PFS). We monitored the dynamics of target lesions and peripheral blood cells at regular intervals through CT scans and routine blood tests during the treatment process. We present patient responses to ALK inhibitor-based targeted therapy with uterine IMT harboring ALK-IGFBP5 fusion, and the neutrophil-to-lymphocyte ratio (NLR) may be an effective indicator to predict prognosis.

Uterine inflammatory myofibroblastic tumor presented as abnormal uterine bleeding: Two cases report and literature review

RATIONALE

Inflammatory myofibroblastic tumor (IMT) is an extremely rare soft tissue neoplasm consisting of the proliferation of fibroblastic-myofibroblastic cells with inflammatory infiltrates. It is known to occur in many parts of the body and can generally present with benign or locally recurrent behavior. Anaplastic lymphoma kinase is a specific diagnostic marker for IMT, and approximately 50% of IMT patients have anaplastic lymphoma kinase gene rearrangements. Reports of the female genital tract are rare.

PATIENT CONCERNS

Two patients (a 32-year-old multigravida and a 22-year-old nullipara) visited our clinic because of abnormal uterine bleeding and a uterine mass.

DIAGNOSES

Histopathological examination, immunohistochemical markers, and fluorescence in situ hybridization confirmed the presence of a rare uterine IMT.

INTERVENTIONS

The masses were completely resected via hysteroscopy. The multigravida recurred rapidly in terms of symptoms and images, whereas the nullipara was complaint-free during the follow-up period. Finally, the multigravida underwent hysterectomy and bilateral salpingectomies.

OUTCOMES AND LESSONS

Uterine IMTs can be easily overlooked because of their extremely low incidence rate and insufficient awareness among clinicians; however, uterine IMTs need to be considered in the differential diagnosis of uterine masses. Possible differences in the biological behavior of IMT may exist in different individuals.

Histopathologic and Molecular Characterization of Uterine Leiomyoma-like Inflammatory Myofibroblastic Tumor: Comparison to Molecular Subtypes of Uterine Leiomyoma

Uterine leiomyoma (UL) is a common benign neoplasm which can sometimes be difficult to differentiate from the uterine inflammatory myofibroblastic tumor (IMT) based on morphology alone. IMT is a myofibroblastic/fibroblastic neoplasm which has typically been considered to be rare in the uterus. Its clinical behavior is usually indolent although aggressive variants exist. The majority of IMTs harbor genomic rearrangement of anaplastic lymphoma kinase ( ALK ), while ALK fusion has not been thus far detected in ULs. We analyzed 2263 ULs of which 9 (0.4%) had tyrosine-kinase activation. Seven of the samples were ALK immunopositive: 6 had an ALK fusion gene and 1 overexpressed an ALK transcript skipping exons 2 to 3, Moreover, 1 sample had a RET , and 1 a PDGFRB fusion gene. While no recurrent somatic mutations were found, 1 patient had an ALK germline mutation. Seven tumors showed leiomyoma-like morphology, 1 tumor had slightly loose, and 1 fibrous growth pattern. Six tumors had mild to moderate lymphocyte infiltration, while no immune cell infiltration was detected in 3 cases. None of the tumors showed aggressive behavior. Except for strong ALK positivity (7/9 tumors) the protein expression profile of the tumors was identical to ULs and distinct from other mesenchymal uterine tumors. In gene expression level, these tumors and the known UL subclasses did not separate perfectly. However, vitamin C metabolism and epithelial-mesenchymal transition pathways were uniquely enriched in these lesions. The overall similarity of the analyzed tumors to UL raises the question whether an UL diagnosis would be more proper for a subset of uterine IMTs.

Update on Uterine Mesenchymal Neoplasms

This review focuses on recent advances in epithelioid and myxoid uterine mesenchymal neoplasms, a category of tumors whereby diagnostic criteria have been rapidly evolving due to advances in molecular testing. Pertinent clinicopathological and molecular features are highlighted for perivascular epithelioid cell tumors, uterine tumors resembling ovarian sex cord tumors, BCOR/BCORL1-altered high-grade endometrial stromal sarcomas, and inflammatory myofibroblastic tumors. Novel developments in epithelioid and myxoid leiomyosarcomas are briefly discussed, and differential diagnoses with key diagnostic criteria are provided for morphologic mimickers.

Epithelioid Leiomyosarcoma of the Uterus: Modern Outcome-based Appraisal of Diagnostic Criteria in a Large Institutional Series

Epithelioid leiomyosarcoma of the uterus is rare and poorly understood. Herein, we characterize a large institutional series of epithelioid leiomyosarcomas aiming to define outcome-determinant diagnostic pathologic features. We also retrieved epithelioid smooth muscle tumors of unknown malignant potential and evaluated a consecutive cohort of leiomyomas for epithelioid subtypes. Of a total of 1177 uterine leiomyosarcomas, 81 (7%) were categorized as epithelioid after review. Epithelioid leiomyosarcoma was strictly defined as having round to polygonal cells with visible pink cytoplasm and round to ovoid nuclei in ≥50% of the tumor volume. Average age was 55 years (range: 26 to 81 y). Median tumor size was 11 cm; tumor was >5 cm in 93% of subjects; 47% were stage 1 at presentation. An infiltrative tumor border was observed, grossly and/or microscopically, in 89% of cases; necrosis was noted in 80%, and vascular invasion in 47%. Mitotic count in 2.4 mm2 (totalling 10 high-power fields, each field 0.55 mm in diameter) ranged from 3 to 100 (median: 26). All cases had moderate, severe or highly pleomorphic atypia. All cases had 2 or 3 of the following: necrosis, at least moderate atypia and ≥4 mitoses in 2.4 mm2. Immunohistochemistry revealed frequent expression of smooth muscle markers including SMA (96%), desmin (95%), and caldesmon (81%). HMB45 and Melan-A were negative in 92% and 100% of cases, respectively. Estrogen and progesterone receptors were expressed by 65% and 54% of tumors, respectively. Follow-up information was available in 68 subjects (median: 23 mo, range: 1 to 254); cancer-related death occurred in 63%, and an additional 15% had recurrent or metastatic disease at last follow-up. Disease-specific survival was shorter in epithelioid leiomyosarcoma patients (median: 44  mo; 35% at 5-y) than in a matched cohort of nonepithelioid leiomyosarcoma (median: 55 mo; 46% at 5-y) (P=0.03). Three epithelioid smooth muscle tumors of unknown malignant potential were evaluated, all <5 cm in size and with atypia and/or irregular borders but mitotic count below the threshold for malignancy. Two of these had follow-up available, which was uneventful. Of 142 consecutive leiomyomas assessed, none had epithelioid morphology as defined. Epithelioid leiomyosarcoma is an aggressive neoplasm, sometimes with a remarkably low mitotic count. In the setting of an epithelioid smooth muscle tumor of the uterus, we postulate that the diagnosis of malignancy is made in the presence of ≥2 of the following: moderate or severe atypia, ≥4 mitoses/2.4 mm2 and tumor cell necrosis. In their absence, the finding of tumor size ≥5 cm, vascular invasion, infiltrative edges or atypical mitoses should be treated with caution, and designation as of at least uncertain malignant potential is warranted.

Uterine inflammatory myofibroblastic tumor: First report of a ROS1 fusion

Inflammatory myofibroblastic tumor (IMT) of the uterus is an uncommon mesenchymal neoplasm that frequently harbors ALK rearrangements. In this report, we describe the first uterine IMT with a FN1-ROS1 fusion, which occurred in a 43-year-old woman who presented with menorrhagia. Morphologically, the well-circumscribed 3 cm tumor was comprised of compact and myxoid foci of relatively bland spindle cells admixed with scattered chronic inflammatory cells limited to the myxoid areas. ROS1 showed moderate cytoplasmic granular staining in < 30% of cells in the myxoid foci, while ALK was negative. RNA sequencing detected a FN1-ROS1 rearrangement that fused FN1 exon 37 to ROS1 exon 34. Although non-ALK-rearranged uterine IMTs are exceedingly rare, this example highlights the importance of performing ROS1 immunohistochemistry and/or molecular analysis in ALK-negative uterine neoplasms morphologically compatible with IMT.