Intraductal carcinomas of the salivary glands: systematic review and classification of 93 published cases

A challenging case of sclerosing polycystic adenoma of the parotid gland: a case report and brief review of the latest updates

Sclerosing polycystic adenoma (SPA) is a rare neoplastic salivary gland lesion with only about 100 cases reported worldwide so far. The lesion is confused with several malignant and other benign tumors such as apocrine intraductal carcinoma (IC), salivary duct carcinoma (SDC), chronic sclerosing sialadenitis, polycystic dysgenetic disease (PDD), pleomorphic adenoma (PA), acinic cell carcinoma (ACC), and mucoepidermoid carcinoma (MEC). We present a case of SPA for a 23-year-old male patient presenting with a slowly growing parotid mass. Fine needle aspiration (FNA) followed by total excision of the tumor was performed and the picture was consistent with SPA. We discuss the findings of the case and briefly review the literature on SPA.

Low-grade intraductal carcinoma in minor salivary glands: A case report and clinical insights

Rationale

Low-grade intraductal carcinoma (LG-IC), is a rare malignant tumour of the salivary glands which has a very good prognosis and must be differentiated from the other types of salivary gland malignant tumours, which have a totally different behaviour and a worse prognosis.

Patient Concerns

A case is presented of a 52-year-old woman who was first diagnosed and treated in another clinic in 2019 for an LG-IC in the left submandibular gland space. Two years later, she was admitted to our department with a new lesion, this time in the upper jaw lip on the left side, which also turned out to be LG-IC.

Diagnosis

Magnetic resonance imaging and positron emission tomography-computed tomography were performed in order to diagnose and adequately stage the disease prior to the therapeutic intervention.

Outcomes

A 6-month follow-up reveals no sign of recurrence.

Takeaway Lessons

Literature on this rare histopathological entity, as well as the differential diagnosis with the other malignant lesions of the salivary glands and the frequency of metastasis, were reviewed.

Salivary Gland Intraductal Carcinoma: How Do 183 Reported Cases Fit Into a Developing Classification

Salivary gland intraductal carcinoma (IDC) is a very uncommon group of neoplasms. Many names, variations in diagnostic criteria, and newly observed molecular findings (including NCOA4 :: RET , TRIM27 :: RET , HRAS point mutations, and PIK3CA pathway alterations) have generated further confusion in being able to recognize and categorize this group of tumors. Different histologic appearances and patterns of growth suggest there is more than one tumor category, with intercalated duct, apocrine, oncocytic, and hybrid features seen. Frankly destructive invasion further complicates the category, as the name "intraductal" would suggest an "in situ" neoplasm. Recent evidence on fusion-positive IDC demonstrates the same molecular underpinnings in both the ductal and the myoepithelial cells, which aids in further separating these tumors. This article summarizes the historical group of 183 neoplasms classified under the umbrella of IDC and highlights the unique histologic, immunohistochemistry, and molecular features that may further guide nomenclature standardization and harmonization.

Intraductal carcinoma of right parapharyngeal space presenting as a fluctuant swelling of retromolar region: Case emphasizing on the histological differential diagnosis

Intraductal carcinoma (IDC) of salivary gland is an extremely rare malignancy affecting mainly the parotid glands. Intraoral occurrence is seen mainly on the palate where the tumour arises from the minor salivary glands. No previous case has been described in parapharyngeal space. We report a case of low-grade IDC of the anterior compartment of the right parapharyngeal space that clinically resembled a lesion of vascular origin. Due to the extreme rarity of intraductal carcinoma, it may not be considered by dentists and dental specialists in clinical differential diagnoses, leading to delay in treatment. Intraductal carcinoma must be differentiated from its close histological but high-grade mimickers to avoid unnecessary overtreatment and better patient outcome.

Bronchial salivary gland–type intraductal carcinoma with KIAA1217::RET gene fusion composed of intercalated and oncocytic components

Salivary gland-type intraductal carcinoma (IC) is a rare malignant salivary gland neoplasm. Primary salivary gland-type IC has never been described in the lung. Herein, we present a primary pulmonary IC in a 63-year-old woman. The tumor originated in the bronchus wall of the right middle lobe. The tumor consisted of two histological types, intercalated component and oncocytic component. The intercalated component showed tubular/cystic pattern composed of column to cube-shaped cells and scattered mucous cells. The oncocytic component showed solid nests composed of large cells with abundant eosinophilic granular cytoplasm. Immunohistochemically, both histological components were positive for cytokeratin 7 (CK7), S-100 protein, SOX10, and mammaglobin. The rimming myoepithelial cells were highlighted by p63 and smooth muscle actin (SMA). The tumor cells were negative for androgen receptor (AR), HER-2, Dog-1, TTF-1, napsin A, GCDFP-15, and GATA3. In the present case, we detected KIAA1217::RET fusion via DNA-based next-generation sequencing (NGS) and RT-PCR, which established the diagnosis of IC at a molecular level. The present case expands the categories of bronchopulmonary salivary gland-type tumors.

Cystic Salivary Gland Neoplasms: Diagnostic Approach With a Focus on Ancillary Studies

Cystic salivary gland cytology can be challenging due to the fact that a cystic mass can be the clinical presentation of both non-neoplastic and neoplastic conditions. Neoplastic lesions consist of both benign and malignant neoplasms. The cytomorphologic features of these entities can overlap and the cystic background may additionally contribute to the complexity of these lesions and their interpretation. Ancillary studies have been reported in several studies to be beneficial in further characterization of the cellular components and subsequent diagnosis of the cystic lesions of the salivary gland. Fluorescence in situ hybridization, real-time polymerase chain reaction, and next-generation sequencing are now being utilized to detect molecular alterations in salivary gland neoplasms. MALM2 rearrangement is the most common gene fusion in mucoepidermoid carcinoma. PLAG1 rearrangement is present in more than half of pleomorphic adenomas. AKT1:E17K mutation is the key diagnostic feature of the mucinous adenocarcinoma. NR4A3 overexpression is highly sensitive and specific for the diagnosis of acinic cell carcinoma. MYB fusion is noted in adenoid cystic carcinoma. ETV6:NTRK3 fusion is helpful in diagnosis of secretory carcinoma. p16 and human papillomavirus (HPV) studies differentiate HPV-related squamous cell carcinoma from non-HPV-related neoplasms with overlapping features. NCOA4:RET fusion protein is the main fusion in intraductal carcinoma.

S-100 Immunohistochemical Positivity in Rhabdomyoma: An Underestimated Potential Diagnostic Pitfall in Routine Practice

A 66-year-old man presented with a 2.8 cm lesion of the left vocal cord. On contrast-enhanced computed tomography scans, the tumor extended to the supraglottis, subglottis, paraglottic space and anterior commissure, causing partial obstruction of the laryngeal lumen. At another hospital, a fragmented incisional biopsy was diagnosed as a granular cell tumor, as to the S-100 immunohistochemical positivity. After excision, the tumor revealed to be an adult-type laryngeal rhabdomyoma. The typical cytoplasmic rod-like inclusions and cross striations were more evident in the second specimen. We confirmed the unusual S-100 immunohistochemical positivity (variable intensity, >90% of tumor cells). Muscle markers were not performed on the previous biopsy, resulting positive in our specimen (Desmin: strong, diffuse expression; Smooth Muscle Actin: strong staining in 10% of tumor cells). Melan-A, CD68, GFAP, pan-cytokeratins, CEA, calretinin and neurofilaments resulted negative. To our brief, systematic literature review, S-100 positivity (usually variable, often weak or patchy/focal) was globally found in 19/34 (56%) adult-type rhabdomyomas of the head and neck region. Especially on fragmented biopsy material, the differential diagnoses of laryngeal rhabdomyomas may include granular cell tumors, oncocytic tumors of the salivary glands or of different origin, and paragangliomas.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review (Part 6): Correlation of PD-L1 Expression with the Status of Mismatch Repair System, BRCA, PTEN, and Other Genes

Pembrolizumab (anti-PD-1) is allowed in selected metastatic castration-resistant prostate cancer (PC) patients showing microsatellite instability/mismatch repair system deficiency (MSI-H/dMMR). BRCA1/2 loss-of-function is linked to hereditary PCs and homologous recombination DNA-repair system deficiency: poly-ADP-ribose-polymerase inhibitors can be administered to BRCA-mutated PC patients. Recently, docetaxel-refractory metastatic castration-resistant PC patients with BRCA1/2 or ATM somatic mutations had higher response rates to pembrolizumab. PTEN regulates cell cycle/proliferation/apoptosis through pathways including the AKT/mTOR, which upregulates PD-L1 expression in PC. Our systematic literature review (PRISMA guidelines) investigated the potential correlations between PD-L1 and MMR/MSI/BRCA/PTEN statuses in PC, discussing few other relevant genes. Excluding selection biases, 74/677 (11%) PCs showed dMMR/MSI; 8/67 (12%) of dMMR/MSI cases were PD-L1+. dMMR-PCs included ductal (3%) and acinar (14%) PCs (all cases tested for MSI were acinar-PCs). In total, 15/39 (39%) PCs harbored BRCA1/2 aberrations: limited data are available for PD-L1 expression in these patients. 13/137 (10%) PTEN- PCs were PD-L1+; 10/29 (35%) PD-L1+ PCs showed PTEN negativity. SPOP mutations may increase PD-L1 levels, while the potential correlation between PD-L1 and ERG expression in PC should be clarified. Further research should verify how the efficacy of PD-1 inhibitors in metastatic castration-resistant PCs is related to dMMR/MSI, DNA-damage repair genes defects, or PD-L1 expression.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 7: PD-L1 Expression in Liquid Biopsy

Liquid biopsy is an accessible, non-invasive diagnostic tool for advanced prostate cancer (PC) patients, potentially representing a real-time monitoring test for tumor evolution and response to treatment through the analysis of circulating tumor cells (CTCs) and exosomes. We performed a systematic literature review (PRISMA guidelines) to describe the current knowledge about PD-L1 expression in liquid biopsies of PC patients: 101/159 (64%) cases revealed a variable number of PD-L1+ CTCs. Outcome correlations should be investigated in larger series. Nuclear PD-L1 expression by CTCs was occasionally associated with worse prognosis. Treatment (abiraterone, enzalutamide, radiotherapy, checkpoint-inhibitors) influenced PD-L1+ CTC levels. Discordance in PD-L1 status was detected between primary vs. metastatic PC tissue biopsies and CTCs vs. corresponding tumor tissues. PD-L1 is also released by PC cells through soluble exosomes, which could inhibit the T cell function, causing immune evasion. PD-L1+ PC-CTC monitoring and genomic profiling may better characterize the ongoing aggressive PC forms compared to PD-L1 evaluation on primary tumor biopsies/prostatectomy specimens (sometimes sampled a long time before recurrence/progression). Myeloid-derived suppressor cells and dendritic cells (DCs), which may have immune-suppressive effects in tumor microenvironment, have been found in PC patients circulation, sometimes expressing PD-L1. Occasionally, their levels correlated to clinical outcome. Enzalutamide-progressing castration-resistant PC patients revealed increased PD-1+ T cells and circulating PD-L1/2+ DCs.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 5: Epigenetic Regulation of PD-L1

Epigenetic alterations (including DNA methylation or miRNAs) influence oncogene/oncosuppressor gene expression without changing the DNA sequence. Prostate cancer (PC) displays a complex genetic and epigenetic regulation of cell-growth pathways and tumor progression. We performed a systematic literature review (following PRISMA guidelines) focused on the epigenetic regulation of PD-L1 expression in PC. In PC cell lines, CpG island methylation of the CD274 promoter negatively regulated PD-L1 expression. Histone modifiers also influence the PD-L1 transcription rate: the deletion or silencing of the histone modifiers MLL3/MML1 can positively regulate PD-L1 expression. Epigenetic drugs (EDs) may be promising in reprogramming tumor cells, reversing epigenetic modifications, and cancer immune evasion. EDs promoting a chromatin-inactive transcriptional state (such as bromodomain or p300/CBP inhibitors) downregulated PD-L1, while EDs favoring a chromatin-active state (i.e., histone deacetylase inhibitors) increased PD-L1 expression. miRNAs can regulate PD-L1 at a post-transcriptional level. miR-195/miR-16 were negatively associated with PD-L1 expression and positively correlated to longer biochemical recurrence-free survival; they also enhanced the radiotherapy efficacy in PC cell lines. miR-197 and miR-200a-c positively correlated to PD-L1 mRNA levels and inversely correlated to the methylation of PD-L1 promoter in a large series. miR-570, miR-34a and miR-513 may also be involved in epigenetic regulation.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 3: PD-L1, Intracellular Signaling Pathways and Tumor Microenvironment

The tumor microenvironment (TME) includes immune (T, B, NK, dendritic), stromal, mesenchymal, endothelial, adipocytic cells, extracellular matrix, and cytokines/chemokines/soluble factors regulating various intracellular signaling pathways (ISP) in tumor cells. TME influences the survival/progression of prostate cancer (PC), enabling tumor cell immune-evasion also through the activation of the PD-1/PD-L1 axis. We have performed a systematic literature review according to the PRISMA guidelines, to investigate how the PD-1/PD-L1 pathway is influenced by TME and ISPs. Tumor immune-escape mechanisms include suppression/exhaustion of tumor infiltrating cytotoxic T lymphocytes, inhibition of tumor suppressive NK cells, increase in immune-suppressive immune cells (regulatory T, M2 macrophagic, myeloid-derived suppressor, dendritic, stromal, and adipocytic cells). IFN-γ (the most investigated factor), TGF-β, TNF-α, IL-6, IL-17, IL-15, IL-27, complement factor C5a, and other soluble molecules secreted by TME components (and sometimes increased in patients' serum), as well as and hypoxia, influenced the regulation of PD-L1. Experimental studies using human and mouse PC cell lines (derived from either androgen-sensitive or androgen-resistant tumors) revealed that the intracellular ERK/MEK, Akt-mTOR, NF-kB, WNT and JAK/STAT pathways were involved in PD-L1 upregulation in PC. Blocking the PD-1/PD-L1 signaling by using immunotherapy drugs can prevent tumor immune-escape, increasing the anti-tumor activity of immune cells.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 1: Focus on Immunohistochemical Results with Discussion of Pre-Analytical and Interpretation Variables

Immunotherapy targeting the PD-1-PD-L1 axis yielded good results in treating different immunologically ''hot'' tumors. A phase II study revealed good therapeutic activity of pembrolizumab in selected prostatic carcinoma (PC)-patients. We performed a systematic literature review (PRISMA guidelines), which analyzes the immunohistochemical expression of PD-L1 in human PC samples and highlights the pre-analytical and interpretation variables. Interestingly, 29% acinar PCs, 7% ductal PCs, and 46% neuroendocrine carcinomas/tumors were PD-L1+ on immunohistochemistry. Different scoring methods or cut-off criteria were applied on variable specimen-types, evaluating tumors showing different clinic-pathologic features. The positivity rate of different PD-L1 antibody clones in tumor cells ranged from 3% (SP142) to 50% (ABM4E54), excluding the single case tested for RM-320. The most tested clone was E1L3N, followed by 22C3 (most used for pembrolizumab eligibility), SP263, SP142, and 28-8, which gave the positivity rates of 35%, 11-41% (depending on different scoring systems), 6%, 3%, and 15%, respectively. Other clones were tested in <200 cases. The PD-L1 positivity rate was usually higher in tumors than benign tissues. It was higher in non-tissue microarray specimens (41-50% vs. 15%), as PC cells frequently showed heterogenous or focal PD-L1-staining. PD-L1 was expressed by immune or stromal cells in 12% and 69% cases, respectively. Tumor heterogeneity, inter-institutional preanalytics, and inter-observer interpretation variability may account for result biases.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 4: Experimental Treatments in Pre-Clinical Studies (Cell Lines and Mouse Models)

In prostate cancer (PC), the PD-1/PD-L1 axis regulates various signaling pathways and it is influenced by extracellular factors. Pre-clinical experimental studies investigating the effects of various treatments (alone or combined) may discover how to overcome the immunotherapy-resistance in PC-patients. We performed a systematic literature review (PRISMA guidelines) to delineate the landscape of pre-clinical studies (including cell lines and mouse models) that tested treatments with effects on PD-L1 signaling in PC. NF-kB, MEK, JAK, or STAT inhibitors on human/mouse, primary/metastatic PC-cell lines variably down-modulated PD-L1-expression, reducing chemoresistance and tumor cell migration. If PC-cells were co-cultured with NK, CD8+ T-cells or CAR-T cells, the immune cell cytotoxicity increased when PD-L1 was downregulated (opposite effects for PD-L1 upregulation). In mouse models, radiotherapy, CDK4/6-inhibitors, and RB deletion induced PD-L1-upregulation, causing PC-immune-evasion. Epigenetic drugs may reduce PD-L1 expression. In some PC experimental models, blocking only the PD-1/PD-L1 pathway had limited efficacy in reducing the tumor growth. Anti-tumor effects could be increased by combining the PD-1/PD-L1 blockade with other approaches (inhibitors of tyrosine kinase, PI3K/mTOR or JAK/STAT3 pathways, p300/CBP; anti-RANKL and/or anti-CTLA-4 antibodies; cytokines; nitroxoline; DNA/cell vaccines; radiotherapy/Radium-223).

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review. Part 2: Clinic-Pathologic Correlations

Many studies have investigated the potential prognostic and predictive role of PD-L1 in prostatic carcinoma (PC). We performed a systematic literature review (PRISMA guidelines) to critically evaluate human tissue-based studies (immunohistochemistry, molecular analysis, etc.), experimental research (cell lines, mouse models), and clinical trials. Despite some controversial results and study limitations, PD-L1 expression by tumor cells may be related to clinic-pathologic features of adverse outcome, including advanced tumor stage (high pT, presence of lymph node, and distant metastases), positivity of surgical margins, high Grade Group, and castration resistance. Different PD-L1 positivity rates may be observed in matched primary PCs and various metastatic sites of the same patients. Over-fixation, type/duration of decalcification, and PD-L1 antibody clone may influence the immunohistochemical analysis of PD-L1 on bone metastases. PD-L1 seemed expressed more frequently by castration-resistant PCs (49%) as compared to hormone-sensitive PCs (17%). Some series found that PD-L1 positivity was associated with decreased time to castration resistance. Treatment with ipilimumab, cyclophosphamide/GVAX/degarelix, or degarelix alone may increase PD-L1 expression. Correlation of PD-L1 positivity with overall survival and outcomes related to tumor recurrence were rarely investigated; the few analyzed series produced conflicting results and sometimes showed limitations. Further studies are required. The testing and scoring of PD-L1 should be standardized.

Intraductal carcinoma of the salivary gland with NCOA4-RET: expanding the morphologic spectrum and an algorithmic diagnostic approach

After the publication of the 2017 World Health Organization Classification of Head and Neck Tumours, there has been increasing interest in the classification of newly categorized intraductal carcinomas. Intraductal carcinoma (IC) is an indolent tumor, typically arising in the parotid gland, with an intact myoepithelial layer and a cystic, papillary, often cribriform architecture. Early studies of IC identified a heterogeneous group of molecular alterations driving neoplasia, and recent studies have defined three primary morphological/immunohistochemical variants, subsequently linking these morphologic variants with defined molecular signatures. Although studies to date have pointed toward distinct molecular alterations after histological classification, this study used a novel approach, focusing primarily on six cases of IC with NCOA4-RET gene rearrangement as determined by next-generation sequencing and describing the spectrum of clinicopathologic findings within that molecularly-defined group, among them a unique association between the NCOA4-RET fusion and hybrid variant IC and the first case of IC arising in association with a pleomorphic adenoma. RET-rearranged IC show histological and immunohistochemical overlap with the more widely recognized secretory carcinoma, including low-grade morphology, a lumen-forming or microcystic growth pattern, and co-expression of S100, SOX10, and mammaglobin, findings undoubtedly leading to misdiagnosis. Typically regarded to have ETV6-NTRK3 fusions, secretory carcinomas may alternatively arise with RET fusions as well. Adding our cohort of six NCOA4-RET fusion-positive IC compared with four cases of secretory carcinoma with ETV6-RET fusions and a single case of fusion-negative IC with salivary duct carcinoma-like genetics, we propose a diagnostic algorithm that integrates histological elements, including atypia and invasiveness, and the likelihood of specific molecular alterations to increase diagnostic accuracy in what can be a very subtle diagnosis with important clinical implications.

A rare case of high-grade intraductal carcinoma of the upper lip: immunohistochemical and genetic analyses

Although intraductal carcinoma (IDC) of the salivary glands was previously called low-grade cribriform cystadenocarcinoma, it was newly categorized in the 4th version of the World Health Organization classification. We report a case of IDC of the upper lip and examined it immunohistochemically and genetically. The patient was a 48-year-old Japanese female, who noticed a tiny nodule on her left upper lip. Histologically, the tumor cells, which had eosinophilic cytoplasm, exhibited papillary and solid growth patterns, and regions of suspected microinvasion or intraductal spread were also seen at the periphery of the tumor. Small necrotic foci were noted. Immunohistochemically, the tumor cells were diffusely positive for the androgen receptor, CK19, CK5/6, EGFR, and SOX10, whereas they were focally positive for GCDFP-15, S-100 protein, and mammaglobin. The tumor nests were surrounded by alpha-smooth muscle actin-p63-/calponin-/CK14-positive myoepithelial cells. The Ki-67 labeling index was 51.2%. Genetic analysis showed no evidence of the TRIM27-RET or NCOA4-RET fusion gene. We finally diagnosed the tumor as a high-grade mixed intercalated duct/apocrine-type IDC of the upper lip. IDC of the minor salivary glands is exceedingly rare. We discuss diagnostic problems associated with minor salivary gland lesions, and the "basal-like" phenotype of this case.

Molecular Pathology of Salivary Gland Neoplasms: Diagnostic, Prognostic, and Predictive Perspective

Salivary gland neoplasms are an uncommon and widely heterogeneous group of tumors. In recent years, there has been considerable progress in efforts to reveal the molecular landscape of these tumors, although it is still limited and appears to be only the tip of the iceberg. Genomic aberrations, especially specific chromosomal rearrangements including CRTC1-MAML2 and CRTC3-MAML2 in mucoepidermoid carcinoma, MYB-NFIB and MYBL1-NFIB fusions in adenoid cystic carcinoma, PLAG1 and HMGA2 alterations in pleomorphic adenoma and carcinoma ex pleomorphic adenoma, ETV6-NTRK3 and ETV6-RET in secretory carcinoma, EWSR1-ATF1 and EWSR1-CREM in clear cell carcinoma, provide new insights into the molecular pathogenesis of various salivary gland neoplasms and help to better classify them. These genetic aberrations primarily serve as diagnostic tools in salivary gland tumor diagnosis; however, some also have promise as prognostic or predictive biomarkers. This review summarizes the latest developments in molecular pathology of salivary gland tumors with a focus on distinctive molecular characteristics.

How Can We Treat Vulvar Carcinoma in Pregnancy? A Systematic Review of the Literature

According to our systematic literature review (PRISMA guidelines), only 37 vulvar squamous cell carcinomas (VSCCs) were diagnosed during pregnancy (age range: 17-41 years). The tumor size range was 0.3-15 cm. The treatment was performed after (14/37, 38%), before (10/37, 27%), or before-and-after delivery (11/37, 30%). We found that 21/37 (57%) cases were stage I, 2 II (5%), 11 III (30%), and 3 IVB (8%). HPV-related features (condylomas/warts; HPV infection; high-grade squamous intraepithelial lesion) were reported in 11/37 (30%) cases. We also found that 9/37 (24%) patients had inflammatory conditions (lichen sclerosus/planus, psoriasis, chronic dermatitis). The time-to-recurrence/progression (12/37, 32%) ranged from 0 to 36 (mean 9) months. Eight women died of disease (22%) 2.5-48 months after diagnosis, 2 (5%) were alive with disease, and 23 (62%) were disease-free at the end of follow-up. Pregnant patients must be followed-up. Even if they are small, newly arising vulvar lesions should be biopsied, especially in women with risk factors (HPV, dermatosis, etc.). The treatment of VSCCs diagnosed in late third trimester might be delayed until postpartum. Elective cesarean section may prevent vulvar wound dehiscence. In the few reported cases, pregnancy/fetal outcomes seemed to not be affected by invasive treatments during pregnancy. However, clinicians must be careful; larger cohorts should define the best treatment. Definite guidelines are lacking, so a multidisciplinary approach and discussion with patients are mandatory.

Low-Grade Intraductal Carcinoma of the Parotid Gland: A Case Report and Literature Review

Low-grade intraductal carcinoma is a rare neoplasia with an excellent prognosis, previously classified as low-grade cribriform cystadenocarcinoma and low-grade salivary duct carcinoma. The tumor mainly occurs in the parotid gland and presents a ductal phenotype and an intraductal/intracystic growth pattern. It resembles intraductal breast lesions such as atypical ductal hyperplasia, papillary and cribriform ductal carcinoma in situ. Despite its infrequency, discriminating low-grade intraductal carcinoma from other salivary gland tumors is crucial, especially because of its favorable prognosis. A 74-year-old woman with a history of neurofibromatosis underwent a superficial parotidectomy to remove a sharply demarcated multi-cystic mass, diagnosed as category 4 at FNAC. The histological examination revealed a demarcated but unencapsulated lesion composed of a bigger cyst surrounded by several smaller cysts, lined by a monolayer or bilayer epithelium alternated with a cribriform proliferation, characterized by "Roman-bridges", with occasional micro-papillae. A myoepithelial component, with a basal disposition, was present, confirmed by intense staining for protein p63 and SMA. Immunohistochemical stains showed intense, strong uniform positivity for pan-cytokeratin, protein S100, and SOX10. The Ki67 proliferation index was low (< 10%). A diagnosis of Low-grade Intraductal Carcinoma (LGIC) of the parotid was made. We performed a literature search in PUBMED for "Intraductal carcinoma", "Low-grade Intraductal Carcinoma", "Cribriform Cystadenocarcinoma", "Salivary Duct Carcinoma", and "Low-Grade Salivary Duct Carcinoma". We selected 17 papers published between 1983 and 2020; the most affected anatomical site was the parotid gland (77/90), followed by minor salivary glands (6/90), the intraparotid lymph nodes (3/90) and the submandibular gland (4/90). Their main histopathological features are reported in the paper. Here we present a case report and a review of scientific literature on this topic to provide some essential diagnostic tools to discriminate this rare entity.

RET Gene Fusions in Malignancies of the Thyroid and Other Tissues

Following the identification of the BCR-ABL1 (Breakpoint Cluster Region-ABelson murine Leukemia) fusion in chronic myelogenous leukemia, gene fusions generating chimeric oncoproteins have been recognized as common genomic structural variations in human malignancies. This is, in particular, a frequent mechanism in the oncogenic conversion of protein kinases. Gene fusion was the first mechanism identified for the oncogenic activation of the receptor tyrosine kinase RET (REarranged during Transfection), initially discovered in papillary thyroid carcinoma (PTC). More recently, the advent of highly sensitive massive parallel (next generation sequencing, NGS) sequencing of tumor DNA or cell-free (cfDNA) circulating tumor DNA, allowed for the detection of RET fusions in many other solid and hematopoietic malignancies. This review summarizes the role of RET fusions in the pathogenesis of human cancer.