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To the Editor.--The authors of "International Medical Graduates and the Shortage of US Pathologists" (1) cite superseded research in declaring a substantial decline in the number of active pathologists practicing [...]

Context.--There has long been debate about whether and when there may be a shortage of pathologists in the United States. One way to assess this is to survey the hiring experiences of pathology practices. A 2018 survey revealed a strong demand for pathologists, with expectations of continued strength. This study updates that prior analysis using data from a 2021 survey of pathology practice leaders. Objective.--To assess the US pathologist job market and examine implications. Design.--We analyzed data from the 2021 College of American Pathologists Practice Leader Survey. This survey queried practice leaders, including regarding the hiring of pathologists, the level of experience being sought, success in filling positions, and expectations for hiring in the next 3 years. Results.--Among the 375 surveyed practice leaders (about one-third of all US pathology practices), 282 provided information about pathologist hiring in 2021. A total of 157 of these 282 practices (55.7%) sought to hire at least 1 pathologist in 2021, up from 116 of 256 practices (45.3%) in 2017; the mean number of pathologists hired per practice also increased. In 2021, a total of 175 of 385 positions (45.5%) were to fill new positions, compared with 95 of 249 positions (38.2%) in 2017. Most practice leaders were comfortable hiring pathologists with less than 2 years of posttraining experience. Practice leaders anticipated continued strong demand for hiring pathologists during the next 3 years. Conclusions.--Our analysis confirms that the demand in pathologist hiring is strong and much increased from 2017. We believe, in combination with other job market indicators, that demand may outstrip the supply of pathologists, which is limited by the number of trainees and has remained constant during the past 20 years. doi: 10.5858/arpa.2022-0023-CP, About 20 years ago, a future shortage in pathologists was predicted as a consequence of the closure of residency programs. (1,2) A decade later, some of the authors of the [...]

The study of male and female reproductive tract development requires expertise in two separate disciplines, developmental biology and endocrinology. For ease of experimentation and economy, the mouse has been used extensively as a model for human development and pathogenesis, and for the most part similarities in developmental processes and hormone action provide ample justification for the relevance of mouse models for human reproductive tract development. Indeed, there are many examples describing the phenotype of human genetic disorders that have a reasonably comparable phenotype in mice, attesting to the congruence between mouse and human development. However, anatomic, developmental and endocrinologic differences exist between mice and humans that (1) must be appreciated and (2) considered with caution when extrapolating information between all animal models and humans. It is critical that the investigator be aware of both the similarities and differences in organogenesis and hormone action within male and female reproductive tracts so as to focus on those features of mouse models with clear relevance to human development/pathology. This review, written by a team with extensive expertise in the anatomy, developmental biology and endocrinology of both mouse and human urogenital tracts, focusses upon the significant human/mouse differences, and when appropriate voices a cautionary note regarding extrapolation of mouse models for understanding development of human male and female reproductive tracts.

Development of the human female reproductive tract is reviewed from the ambisexual stage to advanced development of the uterine tube, uterine corpus, uterine cervix and vagina at 22 weeks. Historically this topic has been under-represented in the literature, and for the most part is based upon hematoxylin and eosin stained sections. Recent immunohistochemical studies for PAX2 (reactive with Müllerian epithelium) and FOXA1 (reactive with urogenital sinus epithelium and its known pelvic derivatives) shed light on an age-old debate on the derivation of vaginal epithelium supporting the idea that human vaginal epithelium derives solely from urogenital sinus epithelium. Aside for the vagina, most of the female reproductive tract is derived from the Müllerian ducts, which fuse in the midline to form the uterovaginal canal, the precursor of uterine corpus and uterine cervix an important player in vaginal development as well. Epithelial and mesenchymal differentiation markers are described during human female reproductive tract development (keratins, homeobox proteins (HOXA11 and ISL1), steroid receptors (estrogen receptor alpha and progesterone receptor), transcription factors and signaling molecules (TP63 and RUNX1), which are expressed in a temporally and spatially dynamic fashion. The utility of xenografts and epithelial-mesenchymal tissue recombination studies are reviewed.

The role of tissue interactions was explored to determine whether epithelial differentiation within the developing human reproductive tract is induced and specified by mesenchyme in tissue recombinants composed of mouse vaginal mesenchyme + human uterine tubal epithelium (mVgM+hTubE). The tissue recombinants were grown in DES-treated ovariectomized athymic mice. After 2-4 weeks of in vivo growth, several vaginal specific features were expressed in the human tubal epithelium. The mesenchyme-induced effects included morphological change as well as expression of several immunohistochemical markers. Although the mesenchyme-induced shift in vaginal differentiation in the human tubal epithelium was not complete, the partial induction of vaginal markers in human tubal epithelium verifies the importance of mesenchymal-epithelial interactions in development of the human female reproductive tract. In a separate experiment, DES-induction of uterine epithelial progesterone receptor (PGR) and estrogen receptor 1 (ESR1) was explored in tissue recombinants composed of wild-type or Esr1KO mouse uterine mesenchyme + human fetal uterine epithelium (wt UtM+hUtE and Esr1KO UtM+hUtE). The rationale of this experiment was to determine whether DES-induction of PGR and ESR1 is mediated directly via epithelial ESR1 or indirectly (paracrine mechanism) via mesenchymal ESR1. DES-induction of uterine epithelial ESR1 and PGR in Esr1KO UtM+hUtE tissue recombinants (devoid of mesenchymal ESR1) formally eliminates the paracrine mechanism and demonstrates that DES induction of human uterine epithelial ESR1 and PGR is directly mediated via epithelial ESR1.

Human female fetal reproductive tracts 9.5-22 weeks of gestation were grown for 1 month in ovariectomized athymic adult female mouse hosts that were either untreated or treated continuously with diethylstilbestrol (DES) via subcutaneous pellet. Normal morphogenesis and normal patterns of differentiation marker expression (KRT6, KRT7, KRT8, KRT10, KRT14, KRT19, ESR1, PGR, TP63, RUNX1, ISL1, HOXA11 and α-ACT2) were observed in xenografts grown in untreated hosts and mimicked observations of previously reported (Cunha et al., 2017) non-grafted specimens of comparable age. DES elicited several notable morphological affects: (a) induction of endometrial/cervical glands, (b) increased plication (folding) of tubal epithelium, (c) stratified squamous maturation of vaginal epithelium and (d) vaginal adenosis. DES also induced ESR1 in epithelia of the uterine corpus, cervix and globally induced PGR in most cells of the developing human female reproductive tract. Keratin expression (KRT6, KRT7, KRT8, KRT14 and KRT19) was minimally affected by DES. Simple columnar adenotic epithelium was devoid of TP63 and RUNX1, while DES-induced mature vaginal epithelium was positive for both transcription factors. Another striking effect of DES was observed in grafts of human uterine tube, in which DES perturbed smooth muscle patterning. These results define for the first time IHC protein markers of DES action on the developing human reproductive tract, which provide bio-endpoints of estrogen-induced teratogenesis in the developing human female reproductive tract for future testing of estrogenic endocrine disruptors.

We present a detailed review of the embryonic and fetal development of the human female reproductive tract utilizing specimens from the 5th through the 22nd gestational week. Hematoxylin and eosin (H&E) as well as immunohistochemical stains were used to study the development of the human uterine tube, endometrium, myometrium, uterine cervix and vagina. Our study revisits and updates the classical reports of Koff (1933) and Bulmer (1957) and presents new data on development of human vaginal epithelium. Koff proposed that the upper 4/5ths of the vagina is derived from Müllerian epithelium and the lower 1/5th derived from urogenital sinus epithelium, while Bulmer proposed that vaginal epithelium derives solely from urogenital sinus epithelium. These conclusions were based entirely upon H&E stained sections. A central player in human vaginal epithelial development is the solid vaginal plate, which arises from the uterovaginal canal (fused Müllerian ducts) cranially and squamous epithelium of urogenital sinus caudally. Since Müllerian and urogenital sinus epithelium cannot be unequivocally identified in H&E stained sections, we used immunostaining for PAX2 (reactive with Müllerian epithelium) and FOXA1 (reactive with urogenital sinus epithelium). By this technique, the PAX2/FOXA1 boundary was located at the extreme caudal aspect of the vaginal plate at 12 weeks. During the ensuing weeks, the PAX2/FOXA1 boundary progressively extended cranially such that by 21 weeks the entire vaginal epithelium was FOXA1-reactive and PAX2-negative. This observation supports Bulmer's proposal that human vaginal epithelium derives solely from urogenital sinus epithelium. Clearly, the development of the human vagina is far more complex than previously envisioned and appears to be distinctly different in many respects from mouse vaginal development.

The job market for pathologists has been, and continues to be, of great concern to pathology organizations, to the community of practicing pathologists and pathologists in training, and to medical [...], * Context.--Disagreement exists within the pathology community about the status of the job market for pathologists. Although many agree that jobs in pathology were harder to come by earlier this decade, recent evidence suggests improvement is occurring. Objective.--To assess the state of the job market for pathologists. Design.--We analyzed data from the 2018 College of American Pathologists Practice Leader Survey. This survey contains data from 253 practice leaders on practices' hiring (and retrenchments) in 2017, the skills and level of experience being sought, success in filling those positions, and expectations for hiring in the next 3 years. Results.--Among the surveyed practice leaders, 115 (45.5%) sought to hire at least 1 pathologist in 2017, and together tried to fill 246 full-time equivalent positions that year, of which 93.5 full-time equivalents (38%) were newly created. This hiring was not limited to larger, academic-based practices, but also occurred among smaller practices and practices based in nonacademic hospitals, independent laboratories, and other settings. Although some practices retrenched (60 full-time equivalents in 2017), the net increase was a healthy 187 full-time equivalents. Practices most frequently sought pathologists who had at least 2 years of experience, but the level of experience identified with the 'optimal' candidate varied by desired areas of subspecialty expertise. Practice leaders also reported expected growth in hiring, with the number of positions they hope to fill in the next 3 years exceeding those vacated by retirement. Conclusions.--Our findings support the proposition that the demand for pathologists is strong, at least at the current time. (Arch Pathol Lab Med. 2020;144:420-426; doi: 10.5858/arpa.2019-0356-CP)

Papillary immature metaplasia (PIM) of the uterine cervix, also called immature condyloma, was firstly described in 1992 by Ward et al (1) as a distinct subset of the exophytic low-grade [...], * Context.--Papillary immature metaplasia (PIM) is a known papillary cervical lesion associated with low-risk human papillomavirus (LR-HPV). Objective.--To evaluate additional clinicopathologic features and the HPV genotypes of PIM and discuss the presumptive cell of origin. Design.--A total of 26 PIM cases were evaluated by [p16.sup.INK4a], cytokeratin (CK) 7, and CK17 immunohistochemical stainings. Human papillomavirus genotyping was performed, by using HPV DNA Chip, HPV polymerase chain reaction (PCR), and real-time PCR. Results.--Histologically, PIM forms either a papillary mass (n = 21 of 26, 81%) or a slightly elevated/flat plaque (n = 5, 19%). All cases contain variable amounts of mucinous epithelia within the lesions. Koilocytosis was identified in 15 of the 26 cases (58%). Sixteen cases (61%) were associated with LR-HPV (types 6, 11, or 42), but 3 cases (12%) with high-risk (HR) HPV (16,16/18, and 33), 2 cases (8%) with mixed LR- and HR-HPV (6/16 and 11/58), while 2 cases (8%) were negative, but [p16.sup.INK4a] immunostaining showed nonblock positivity in all cases. Eight (31%) had high-grade squamous intraepithelial lesion (HSIL) in the adjacent mucosa, 4 (50%) of which showed direct continuity. Identical HPV subtypes were confirmed in separately microdissected cases from PIM and adjacent HSIL. Most lesions (n = 24, 92%) expressed CK17 (reserve cell marker) in a bottom-heavy pattern and CK7 (squamocolumnar junction [SCJ] marker) in a top-heavy pattern, while most cases of low-grade squamous intraepithelial lesion (LSIL) were negative for both markers. Conclusions.--Our results suggest that PIM is a distinct subset of LSIL showing a productive HPV infection, but PIM involves the transformation zone and is proximal to SCJ, while LSIL is mostly from ectocervix or distal to the SCJ. doi: 10.5858/arpa.2017-0267-OA