Mesenchymal neoplasms of the uterus (corpus and cervix) encompass a heterogeneous group of tumors with differing morphologies, immunophenotypes and molecular alterations. With the advent of modern molecular techniques, such as next generation sequencing, newly defined genetic abnormalities are being reported in this group of neoplasms. Herein we report the clinicopathological and molecular features of a series of 13 spindle cell sarcomas of the uterus and vagina (10 cervix, 2 uterine corpus, 1 vagina) with morphology resembling fibrosarcoma. After targeted RNA-sequencing, dual FISH fusion and array-CGH analysis, 7 of 13 tumors exhibited NTRK rearrangements (6 TPM3-NTRK1 and 1 EML4-NTRK3) and 3 a COL1A1-PDGFB fusion; in the other 3 neoplasms, all of which were positive with S100 (2 diffuse, 1 focal), we identified no rearrangement. All the NTRK fusion-positive sarcomas were located in the cervix and exhibited diffuse staining with Trk while all the other neoplasms were negative. CD34 was diffusely positive in all 3 of the COL1A1-PDGFB fusion sarcomas. The latter molecular abnormality is identical to that commonly found in dermatofibrosarcoma protuberans and has not been reported previously in uterine mesenchymal neoplasms. We suggest that uterine sarcomas with a morphology resembling fibrosarcoma (and in which leiomyosarcoma and the known molecularly confirmed high-grade endometrial stromal sarcomas have been excluded) can be divided into 3 groups:-an NTRK fusion group, a COL1A1-PDGFB fusion group and a group containing neither of these molecular abnormalities which, on the basis of positive staining with S100, could be tentatively classified as malignant peripheral nerve sheath tumor, although additional molecular studies may identify specific genetic alterations necessitating a nomenclature change. We suggest a diagnostic algorithm when reporting such neoplasms. Identification of these newly described fusion-associated sarcomas is important given the potential for targeted treatments.

Most prior studies of primary diagnosis in surgical pathology using whole slide imaging (WSI) versus microscopy have focused on specific organ systems or included relatively few cases. The objective of this study was to demonstrate that WSI is noninferior to microscopy for primary diagnosis in surgical pathology. A blinded randomized noninferiority study was conducted across the entire range of surgical pathology cases (biopsies and resections, including hematoxylin and eosin, immunohistochemistry, and special stains) from 4 institutions using the original sign-out diagnosis (baseline diagnosis) as the reference standard. Cases were scanned, converted to WSI and randomized. Sixteen pathologists interpreted cases by microscopy or WSI, followed by a wash-out period of ≥4 weeks, after which cases were read by the same observers using the other modality. Major discordances were identified by an adjudication panel, and the differences between major discordance rates for both microscopy (against the reference standard) and WSI (against the reference standard) were calculated. A total of 1992 cases were included, resulting in 15,925 reads. The major discordance rate with the reference standard diagnosis was 4.9% for WSI and 4.6% for microscopy. The difference between major discordance rates for microscopy and WSI was 0.4% (95% confidence interval, −0.30% to 1.01%). The difference in major discordance rates for WSI and microscopy was highest in endocrine pathology (1.8%), neoplastic kidney pathology (1.5%), urinary bladder pathology (1.3%), and gynecologic pathology (1.2%). Detailed analysis of these cases revealed no instances where interpretation by WSI was consistently inaccurate compared with microscopy for multiple observers. We conclude that WSI is noninferior to microscopy for primary diagnosis in surgical pathology, including biopsies and resections stained with hematoxylin and eosin, immunohistochemistry and special stains. This conclusion is valid across a wide variety of organ systems and specimen types.

Purpose Leiomyosarcoma (LMS) is a malignant neoplasm with smooth muscle differentiation. Little is known about its molecular heterogeneity and no targeted therapy currently exists for LMS. Recognition of different molecular subtypes is necessary to evaluate novel therapeutic options. In a previous study on 51 LMS, we identified three molecular subtypes in LMS. The current study was performed to determine whether the existence of these subtypes could be confirmed in independent cohorts. Experimental Design 99 cases of LMS were expression profiled with 3′end RNA-Sequencing (3SEQ). Consensus Clustering was conducted to determine the optimal number of subtypes. Results We identified 3 LMS molecular subtypes and confirmed this finding by analyzing publically available data on 82 LMS from The Cancer Genome Atlas (TCGA). We identified two new FFPE tissue-compatible diagnostic immunohistochemical markers; LMOD1 for subtype I LMS and ARL4C for subtype II LMS. An LMS tissue microarray with known clinical outcome was used to show that subtype I LMS is associated with good outcome in extrauterine LMS while subtype II LMS is associated with poor prognosis in both uterine and extrauterine LMS. The LMS subtypes showed significant differences in expression levels for genes for which novel targeted therapies are being developed, suggesting that LMS subtypes may respond differentially to these targeted therapies. Conclusion We confirm the existence of 3 molecular subtypes in LMS using two independent datasets and show that the different molecular subtypes are associated with distinct clinical outcomes. The findings offer an opportunity for treating LMS in a subtype-specific targeted approach.

Lynch syndrome (LS) is an autosomal dominant inherited disorder caused by germline mutations in DNA mismatch repair (MMR) genes. Mutation carriers are at substantially increased risk of developing cancers of the colorectum and endometrium, among others. Given recent recommendations for universal, cost-effective screening of all patients with newly diagnosed colorectal cancer using MMR protein immunohistochemistry, we evaluated MMR protein expression in a series of endometrial cancers in the general population. A total of 605 consecutive cases of primary endometrial cancer at a single institution (1997 to 2013) were evaluated regardless of age, family history, or histologic features. Evaluation methods consisted of immunohistochemistry for theMMR proteins MLH1,MSH2, MSH6, and PMS2, followed by DNA methylation analysis for cases with MLH1/PMS2 deficiency. Germline mutation testing was performed on a subset of cases. Forty MMR-deficient, nonmethylated endometrial cancers were identified: 3 MLH1/PMS2 and 37 MSH6/MSH2 protein deficiencies. Only 25% occurred in women below 50 years of age (range, 39 to 88 y), 1 of which was in a risk-reducing hysterectomy specimen. Only 15% of patients had a prior history of carcinoma, including only 2 patients with prior colorectal carcinoma. Most (80%) of the endometrial cancers were purely endometrioid; there were 2 mixed endometrioid/mucinous, 1 mucinous, 1 serous, 2 clear cell, and 2 carcinosarcoma cases. When grading was applicable, 40% of the endometrial malignancies were FIGO grade 1, 34% grade 2, and 26% grade 3. Thirteen percent arose in the lower uterine segment, and 23% had tumor-infiltrating lymphocytes. Of the tumors with known germline testing, 41% with a LS-associated germline mutation were not associated with any of the traditional indicators that have been recommended for LS screening (ie, age 50 y or younger, personal/family cancer pedigree that meets Bethesda guideline criteria, presence of MMR-associated tumor morphology, or location in the lower uterine segment). These data suggest that a significant number of LS-associated endometrial carcinomas are missed using clinical, histologic, and locational screening parameters and provide support for universal screening of all newly diagnosed endometrial cancers.

Tumor expression of programmed cell death ligand 1 (PD-L1) is associated with immune evasion in a variety of malignancies, including a subset of triple-negative breast carcinomas, and may mark cancers as susceptible to PD-1/PD-L1 inhibitor therapies. We herein characterize PD-L1 expression in breast cancers across the full range of histomorphologies and investigate its intratumoral heterogeneity and fidelity across primaries and metastases. A total of 245 primary and 40 metastatic (20 nodal, 20 distant) breast carcinomas were evaluated with PD-L1 immunohistochemistry on tissue microarray. Tumor PD-L1 staining was seen in 12% of all primaries including 32% of triple-negative cancers. Staining was common in ductal cancers with medullary (54%), apocrine (27%), and metaplastic features (40%). However, diffuse (>50%) staining was rare (2% of all cancers and 5% of triple negatives). Immune staining was seen in 29% of all primaries and 61% of triple negatives. Tumor expression of PD-L1 was conserved in 94% of matched primary/metastasis pairs, while immune staining showed fidelity in 71%; the remaining cases acquired PD-L1 immune cell expression in the metastasis. Only half of cases with positive tumor staining showed concordance across all analyzed cores. These data demonstrate that PD-L1 expression is prevalent among high-grade, hormone receptor-negative breast cancers with a range of histomorphologies and shows fidelity between primary and metastatic sites in treatment-naive cancers, although acquisition of immune PD-L1 staining in metastases is not uncommon. There is considerable intratumoral heterogeneity in PD-L1 expression, undermining the suitability of core biopsy in the determination of PD-L1 status. Clinical trials are needed to determine PD-L1 staining thresholds required for therapeutic response, as diffuse staining is rare.