The PAX2 gene is a transcription factor that is essential for the development of the urinary system among other transcription factors. The role of PAX2 is highlighted from the seventh week of gestation, when it is involved in development processes and the emergence of nephrons and collecting tubes. Being an important factor in renal development, mutations of this gene can produce severe alterations in the development of the urinary tract, namely congenital anomalies of the kidneys and urinary tract. The first reported cases described with the PAX2 mutation included both renal anomalies and the involvement of other organs, such as the eyes, producing renal coloboma syndrome. Over the years, numerous cases have been reported, including those with only renal and urinary tract anomalies. The aim of this review is to present a summary of pediatric patients described to have mutations in the PAX2 gene to contribute to a better understanding of the genetic mechanism causing anomalies of the kidneys and urinary tract. In this review, we have included only pediatric cases with renal and urinary tract disorders, without the involvement of other organs. From what we know so far from the literature, this is the first review gathering pediatric patients presenting the PAX2 mutation who have been diagnosed exclusively with renal and urinary tract disorders.

PAX2 is a transcription factor expressed during embryogenesis in the eye, ear, CNS, and genitourinary tract, and is one of the major regulators of kidney development. Mutations in this gene are associated with papillorenal syndrome (PAPRS), a genetic condition characterized by optic nerve dysplasia and renal hypo/dysplasia. In the last 28 years, many cohort studies and case reports highlighted PAX2\'s involvement in a large spectrum of kidney malformations and diseases, with or without eye abnormalities, defining the phenotypes associated with PAX2 variants as \"PAX2-related disorders\". Here, we reported two new sequence variations and reviewed PAX2 mutations annotated on the Leiden Open Variation Database 3.0. DNA was extracted from the peripheral blood of 53 pediatric patients with congenital abnormalities of the kidney and urinary tract (CAKUT). PAX2 gene-coding exonic and flanking intronic regions were sequenced with Sanger technology. Two unrelated patients and two twins carrying one known and two unknown PAX2 variations were observed. The frequency of PAX2-related disorders in this cohort was 5.8%, considering all CAKUT phenotypes (16.7% in the PAPRS phenotype and 2.5% in non-syndromic CAKUT). Although PAX2 mutations have a higher frequency in patients with PAPRS or non-syndromic renal hypoplasia, from the review of variants reported to date in LOVD3, PAX2-related disorders are detected in pediatric patients with other CAKUT phenotypes. In our study, only one patient had a CAKUT without an ocular phenotype, but his twin had both renal and ocular involvement, confirming the extreme inter- and intrafamilial phenotypic variability.

Benign and precancerous endometrial hyperplasias (EH) are differentiated according to two alternative histomorphologic classifications: World Health Organization (WHO) or endometrial intraepithelial neoplasia (EIN) system. The 2017 European Society of Gynaecological Oncology guidelines recommend paired box 2 protein (PAX2) immunohistochemistry to identify precancerous EH. However, methods for interpreting immunostaining and diagnostic accuracy are not defined, and the role of PAX2 in endometrial carcinogenesis is unclear. We aimed to assess: (a) PAX2 expression throughout endometrial carcinogenesis, from normal endometrium to benign EH, precancerous EH, and endometrial cancer (EC); (b) the diagnostic accuracy of PAX2 immunohistochemistry in diagnosing precancerous EH, defining criteria for its use.
Electronic databases were searched for from their inception to July 2018. All studies evaluating PAX2 immunohistochemistry in normal endometrium, EH, and EC were included. Univariate comparisons of PAX2 expression were performed with Fisher\'s exact test (significant P < .05). Sensitivity, specificity, positive and negative likelihood ratio, diagnostic odds ratio (DOR), and area under the curve on summary receiver operating characteristic curves were calculated. Subgroup analyses were based on expression thresholds (decrease vs complete loss) and classifications used (WHO vs EIN).
Six studies with 266 normal endometrium, 586 EH, and 114 EC were included. Both decrease and complete loss of PAX2 expression were significantly more common in EC and precancerous EH than benign EH. Diagnostic accuracy was moderate for both PAX2 complete loss and decrease (areas under the curve 0.829 and 0.876, respectively). PAX2 complete loss with EIN system showed the best results (sensitivity = 0.72; specificity = 0.95; DOR = 43.13).
PAX2 seems to behave as a tumor suppressor in endometrial carcinogenesis. PAX2 is an accurate marker of precancerous EH; complete loss of PAX2 and EIN classification appear as the optimal diagnostic criteria.

We herein report a 3-year-old boy presented with chronic kidney disease (CKD) due to PAX2 missense mutation (C to G transversion at position 418 in exon 4).
He attended our clinic with a 3-month history of foamy urine. Upon examination, he had reduced estimated glomerular filtration rate (GFR) and renal atrophy. Genetic investigations revealed that he has inherited a mutated PAX2 gene from his father, who had renal failure at the age of 20. We searched the literature and confirmed that this mutation site has not been reported by any other group before.
Although renal coloboma syndrome (RCS) with simultaneous kidney and eye involvement is the most common phenotype of PAX2 mutations, current literature supports that such mutations may have profuse clinical manifestations and renal hypoplasia is one distinct entity in the spectrum.

Hemangioblastomas are benign tumors of undetermined origin, and account for up to 2.5% of all intracranial tumors. They may occur either sporadically or as a manifestation of von Hippel-Lindau (VHL) syndrome. Central nervous system (CNS) hemangioblastomas are pathologically diagnosed by gross and microscopic morphology, with further support of the diagnosis conferred by a characteristic immunohistochemistry profile including PAX8 negativity. Although renal hemangioblastomas have previously been reported to be PAX8 positive, CNS hemangioblastoma positive PAX8 expression has never been reported. We reviewed 11 cases of cerebellar hemangioblastoma from our institution over a 7-year period (2010 to 2017). Tissue was stained for PAX8 to determine immunohistochemical labeling. Of 11 reviewed cases of cerebellar hemangioblastoma, 7 exhibited PAX8 immunohistochemical expression. A review of the literature found no previously reported cases of positive PAX8 labeling in cerebellar hemangiomas. PAX8 negativity is not as specific for cerebellar hemangioblastoma as previously thought, and caution must be used when relying solely on a panel of PAX2, PAX8, and inhibin A for pathologic diagnosis.

Ovarian cancer is the most common cause of gynecologic cancer death. Both morphologically and immunohistochemically, metastatic mucinous tumors are the best mimickers of mucinous ovarian tumors; its pathogenesis still remains a mystery. PAX2 and PAX8 immunohisyochemistries are useful for differentiating numerous primary tumour types from metastatic ones. There are few studies in literature about PAX expressions in mucinous and seromucinous tumors. None of these are takes into account the histologic type (whether it is seromucinous or mucinous) or the metastatic origin. With this purpose hematoxylin and eosine slides of ovarian mucinous and seromucinous tumors were re-evaluated and one block was chosen for each case. The study included 76 ovarian mucinous and seromucinous tumors of the ovary reported in Hacettepe University department of pathology between 2000 and 2013. Tissue microarray (TMA) was designed from the chosen blocks, PAX2, PAX8, CDX2 immunostains was preformed to the TMA slides. As a result, most of the metastatic cases were negative for PAX2 (91.2 %) and PAX8 (86.3 %), many were diffusely and strongly positive for CDX2 (68.2 %). Seromucinous tumors were devoid of CDX2 expression; but all cases (except one) displayed strong and diffuse positivity with PAX8. In other words differing from mucinous tumors, seromucinous tumors show strong PAX8 positivity-similar to serous tumors. This study shows that PAX8 and CDX2 could be useful in differentiating primary mucinous from metastatic tumor. Furthermore unlike the homogeneity in seromucinous tumors for PAX8 and CDX2 mucinous tumors shows heterogeneity with different expression patterns.

PAX2 is a member of the PAX family of transcription factors that, together with PAX8, is involved in the regulation of the organogenesis of the kidney and the Müllerian system. Recent investigations have demonstrated that, among tumors, PAX2 is commonly expressed in epithelial tumors of the kidney and female genital tract. Although PAX2 expression has also been reported in B-cell lymphomas and rhabdomyosarcomas, especially alveolar rhabdomyosarcomas, it has been suggested that the positivity in these tumors was most probably due to a cross-reactivity of the anti-PAX2 antibody used in those investigations with other members of the PAX protein family. An analysis of published studies indicates that PAX2 sensitivity for epithelial renal neoplasms and epithelial tumors of the female genital tract is lower than that of PAX8. In contrast to the latter marker, however, PAX2 does not appear to be expressed in epithelial tumors of the thyroid gland or thymus. Because of its restricted expression, PAX2 has proved to be a useful immunohistochemical marker with a wide range of diagnostic applications in surgical pathology, some of which will be briefly reviewed.

The diagnosis of metastatic clear cell renal cell carcinoma may be difficult in some cases, particularly in the small image-guided biopsies that are becoming more common. As targeted therapies for renal cell carcinoma are now standard treatment, the recognition and diagnosis of renal cell carcinoma has become even more critical. Many adjunctive immunohistochemical markers of renal epithelial lineage such as CD10 and RCCma have been proposed as aids in the diagnosis of metastatic renal cell carcinoma, but low specificities often limit their utility. More recently described markers (PAX-2, PAX-8, human kidney injury molecule-1, hepatocyte nuclear factor-1-β, and carbonic anhydrase-IX) offer the potential for greater sensitivity and specificity in this diagnostic setting; however, knowledge of their expected staining in other neoplasms and tissues is critical for appropriate use. In this review, we discuss the most widely used immunohistochemical markers of renal lineage with an emphasis on their sensitivity and specificity for metastatic clear cell renal cell carcinoma. Subsequently, we present a variety of organ-specific differential diagnostic scenarios in which metastatic clear cell renal cell carcinoma might be considered and we propose immunopanels for use in each situation.