Mucinous Epithelial Lesions in Endometrial Curettage Material: A Diagnostic Challenge

Special Considerations in Classification and Workup of Endometrial Carcinomas

CONTEXT.—

A variety of uncommon malignant endometrial tumors can be challenging to diagnose because of overlapping morphology with more common entities. In some cases, immunohistochemical stains and/or molecular testing allow for more definitive diagnosis or prognostication.

OBJECTIVE.—

To review classic morphologic features of uncommon endometrial tumors, pathologic features of these tumors and their mimics, and the evidence for use of immunohistochemistry and molecular testing in the diagnosis of these tumors.

DATA SOURCES.—

University of Michigan (Ann Arbor) cases and review of pertinent literature about each entity.

CONCLUSIONS.—

Although each of these uncommon endometrial tumors has morphologic mimics, key histologic features, immunohistochemical stains, and molecular testing allow for accurate classification.

Mucinous Proliferations of the Uterine Corpus: Comprehensive Appraisal of an Evolving Spectrum of Neoplasms

A variety of endometrial lesions may contain mucinous cells. Herein, the author reviews the literature on the classification and clinicopathologic significance of uterine corpus proliferations with a significant mucinous component, assesses the 2020 World Health Organization classification of such lesions, and presents a diagnostic framework. The key epithelial mucinous lesions include mucinous metaplasia, atypical mucinous glandular proliferation and mucinous carcinoma. Each of these categories are classifiable into "usual" and gastrointestinal subtypes, the latter being indicative of intestinal (presence of goblet cells) and/or gastric-type (abundant, pale eosinophilic or clear cytoplasm and well-defined cell borders) morphology. It has been proposed that at least focal expression of gastrointestinal immunohistochemical markers be required for all gastrointestinal type lesions, and for gastrointestinal type atypical mucinous glandular proliferation and carcinoma, minimality or absence of estrogen receptor expression, and the absence of an endometrioid component. Mucinous carcinomas of the usual type, in which >50% of the tumor is comprised of a mucinous component, are the most common. Morphologic subtypes include mucinous carcinoma with microglandular features and mucinous carcinoma with signet rings (signet ring carcinoma). Endometrioid carcinomas with a less than a 50% mucinous component are classified as endometrioid carcinoma with mucinous differentiation. Several studies have directly compared endometrioid and mucinous carcinomas, the latter presumably of the usual type, with respect to patient outcomes after treatment. All have found no difference in overall and disease free survival between these groups. However, three major studies have found mucinous carcinomas to be associated with a higher risk of lymph node metastases. Nineteen cases of mucinous carcinoma of the gastrointestinal type have been reported, and the limited data on their follow-up after primary treatment suggests that this subtype is more clinically aggressive and should accordingly be classified separately from mucinous carcinomas of the usual type. The morphologic spectrum of mucinous carcinoma of the gastrointestinal type is unclear and continues to evolve. Mucinous change, which may sometimes be extensive, may also be associated with papillary proliferation of the endometrium, adenomyoma of the endocervical type, atypical, and typical adenomyomas. In a curettage or biopsy, intestinal type mucinous epithelium may be indicative of any of the gastrointestinal lesions mentioned above, but may also represent samplings of uterine teratomas, yolk sac tumors, genital and extragenital adenocarcinomas with intestinal differentiation, or low-grade appendiceal mucinous neoplasms that secondarily involve the endometrium.

Utility of p63 and PTEN Staining in Distinguishing Cervical Microglandular Hyperplasia from Endometrial Endometrioid Carcinoma with Microglandular/Mucinous Features

Aims

Distinction between well‐differentiated endometrial carcinoma (EMCA) with microglandular/mucinous features and benign endocervical microglandular hyperplasia (MGH) can be a diagnostic challenge, especially when tissue is limited. The immunostains used to distinguish endocervical and endometrial carcinoma are less useful when the differential diagnosis is MGH. Here, we investigate the utility of p63 and phosphatase and tensin homologue (PTEN) to aid accurate classification.

Methods and results

Cases obtained from our pathology archives included 25 EMCA with mucinous/microglandular features, 26 MGH and nine atypical microglandular proliferations. Cases were assessed for glandular architecture, presence of mucinous and/or eosinophilic luminal secretions, subnuclear vacuoles, foamy histiocytes, inflammation, squamous metaplasia, cytological atypia and mitotic activity. The presence and pattern of immunohistochemical staining for p63 and PTEN was recorded. Microglandular proliferations with cytological atypia, mitotic activity, foamy histiocytes and complex glandular architecture were more commonly seen in EMCA, while small glands, bland nuclei and subnuclear vacuoles were enriched in MGH. All MGH cases displayed p63‐positive subcolumnar reserve cells and retained PTEN expression. Four EMCA cases showed non‐specific focal p63 staining either at the surface of the tumour or in areas of squamous differentiation. p63 and PTEN immunostains accurately predicted the final diagnosis for 3 atypical microglandular proliferation cases with follow‐up.

Conclusions

While there are morphological characteristics that differentiate EMCA and MGH, there is frequent overlap between these entities. Nonetheless, the pattern and extent of p63 and PTEN can aid accurate classification. Consistent p63‐positive subcolumnar reserve cells were seen only in MGH.

The diagnosis of mucinous lesions in endometrial samplings by gynaecological pathologists: an analysis of diagnostic reproducibility

The purpose of this study is to assess the reproducibility among gynaecological pathologists in their diagnosis of mucinous alterations in endometrial sampling specimens. Twenty-six cases were independently reviewed by four experienced gynaecological pathologists from four academic medical centres. Pathologists were asked to classify each case into one of four groups, including three World Health Organization (WHO)-recognised categories: (1) mucinous metaplasia; (2) atypical mucinous glandular proliferation; (3) carcinoma; and (4) 'other' (absence of a true mucinous alteration and/or an alteration of non-endometrial origin). The overall reproducibility was 'fair' (κ = 0.39). In an analytical scenario that established three clinically significant groups ('benign/non-neoplastic', 'atypical', and 'carcinoma') by redistributing all group 4 responses, the resultant kappa improved to 0.51 (moderate reproducibility). In another analysis with only two categories-'benign/non-neoplastic' versus 'atypical/carcinoma'-reproducibility was similarly moderate (κ = 0.46). However, with one exception, all cases that were ultimately diagnosed as carcinoma in a follow-up hysterectomy specimen, were classified as atypical or carcinoma in the preceding sampling. For 11 cases that were classified as either 'carcinoma' or 'atypical' by all observers, there was moderate reproducibility (κ = 0.53) in making that distinction, and none of a wide array of morphological features were found to significantly distinguish between these two categories. For five cases that all observers classified as either mucinous metaplasia or benign endocervix, reproducibility was substantial (κ = 0.67). In summary, gynaecological pathologists show moderate reproducibility in categorising mucinous alterations in endometrial sampling specimens as benign, atypical, or carcinomatous. They accurately classify as at least 'atypical' those cases that are ultimately diagnosed as carcinoma in the subsequent resection. Our findings suggest that there are indeed some mucinous alterations which have features that do not allow for reproducible assignment by pathologists into the WHO-recognised categories. In this subset of cases, there may be a need for better-defined diagnostic criteria and/or extra-morphological diagnostic tools.

The clinical significance of K-ras mutation in endometrial "surface epithelial changes" and their associated endometrial adenocarcinoma

OBJECTIVES

The entity of 'surface epithelial changes' (SECs) was first described in 1995 [1]. Morphologically, SECs usually arise from malignant glands at the superficial aspect of well differentiated (WD) endometrioid carcinomas (ECs) and impart the appearance of a 'maturational' phenomenon at the surface of the cancer. Exhibiting a paradoxically bland histologic appearance, SECs typically show morphologic features that mimic benign entities, particularly endocervical microglandular hyperplasia (MGH). SECs have been associated with approximately half of WD endometrioid carcinomas many of which showed focal mucinous differentiation. Despite their morphologically benign histology, some have questioned whether the presence of SECs represents a 'marker' for an underlying malignancy, especially in postmenopausal women with endocervical or MGH-type SECs in their endometrial sampling. Since the biologic nature of SECs is unknown, we aimed to study the prevalence of KRAS gene mutations in SECs and the underlying WD endometrioid adenocarcinomas (EC) from which they directly arise.

METHODS

24 cases with biopsy proven SECs and ECs in their subsequent hysterectomy were retrieved. Genomic DNA was extracted from formalin-fixed paraffin-embedded tissue. PCR amplification for KRAS codons 12 and 13 was performed, followed by sequencing using capillary electrophoresis.

RESULTS

KRAS codons 12 and 13 mutations were detected in 19 of 24 (79%) SECs, and 19 of 24 (79%) ECs. All SECs had the same KRAS mutation as the underlying EC.

CONCLUSIONS

Our results suggest that SECs are of neoplastic origin and that KRAS mutations play an important role in the tumorigenesis of ECs and SECs.

How to approach the many faces of endometrioid carcinoma

This article reviews the salient features of variants of endometrioid carcinoma (ECa) that can pose a diagnostic challenge and/or are associated with unique clinicopathological findings. Variants with distinct architectural and cytologic features include the following: (1) ECa with a villoglandular pattern (tumor with finger-like papillae lined by bland cells with a tendency for vascular/lymphatic invasion and lymph node metastasis once this pattern is seen within the myoinvasive component); (2) papillary ECa of intermediate grade (grade 2) (tumor that can be mistaken for serous carcinoma, as it contains papillae showing slightly irregular contours, moderately atypical cells, and it is associated with vascular/lymphatic invasion/lymph node metastasis, but with common association with mucinous metaplasia, MELF (microcystic, elongated, and fragmented) pattern of invasion, and wild p53 expression); (3) ECa with non-villous papillae (tumor containing pseudopapillae within glands with bland-appearing cytology commonly associated with abortive squamous differentiation and otherwise not different from usual ECa); (4) ECa with microglandular-like pattern (tumor that mimics microglandular hyperplasia of the cervix, often lacking the typical appearance of microglandular hyperplasia and showing Ki-67 index >10%, strong CD10 expression, and negative PAX-2, p63, and CD34); and (5) ECa with sex cord-like formations and hyalinization (tumor with interconnected cords and nests of bland epithelioid and spindled cells that merge with a typical component of low-grade ECa, usually associated with squamous differentiation and hyalinization). This tumor should be distinguished from carcinosarcoma and, in contrast to the latter, it shows nuclear β-catenin expression, ER/PR and patchy p16 positivity, tends to present at a low stage, and has a favorable prognosis and (6) dedifferentiated ECa (tumor showing a low-grade ECa juxtaposed to an undifferentiated carcinoma-the latter characterized by variably sized monotonous, often non-cohesive cells with brisk mitotic activity and usually arranged in sheets). Undifferentiated carcinoma tends to be negative for PAX8 and ER/PR with variable expression of keratins and can be associated with microsatellite instability (may be part of Lynch syndrome). Variants with distinct cytological features include the following: (1) ECa with clear cells (tumors with clearing due to 'clear' (glycogenated) squamous cells, distinct vacuoles, or not otherwise specified. EC with clear cells should be distinguished from clear cell carcinoma by the absence of the variety of architectural patterns, lack of cuboidal/flattened/hobnail cells, and lack of degree of atypia usually detected in clear cell carcinoma. In addition, they are ER/PR positive and Napsin A and p504S negative in contrast to clear cell carcinoma); (2) ECa with spindle cells (tumor with transition from spindle cells to the glandular component of a low-grade ECa. The spindle cells are keratin, ER/PR, and patchy p16 positive and show wild-type p53 expression); (3) ECa with mucinous differentiation (this tumor can be mistaken for a cervical adenocarcinoma, as they have overlapping features. Expression of ER/PR and vimentin in the context of a negative or patchy p16 positivity and the absence of high-risk HPV allows a correct diagnosis).