Reproducibility of Rejection Grading in Uterus Transplantation: A Multicenter Study

Abstract

Background: Diagnosis of rejection after uterus transplantation is based on histopathological examination of ectocervical biopsies. Inflammation at the stromal-epithelial interface is the backbone of the histopathological classification proposed by our group in 2017. However, the reproducibility of this grading scheme has not been tested, and it is unclear whether it covers the full morphological spectrum of rejection.

Methods: We present a multicenter study in which 5 pathologists from 4 uterus transplantation centers performed 2 rounds of grading on 145 and 48 cervical biopsies, respectively. Three of the centers provided biopsies. Additionally, the presence of perivascular stromal inflammation was recorded. During discussions after the first round, further histological lesions (venous endothelial inflammation and apoptosis) were identified for closer evaluation and added to the panel of lesions to score in the second round. All participants completed a questionnaire to explore current practices in handling and reporting uterus transplant biopsies.

Results: Cervical biopsies were commonly performed in all centers to monitor rejection. Intraobserver reproducibility of rejection grading (performed by 1 rater) was excellent, whereas interobserver reproducibility was moderate and did not improve in the second round. Reproducibility of perivascular stromal inflammation was moderate but unsatisfactory for venous endothelial inflammation and apoptosis. All lesions were more frequent in, but not restricted to, biopsies with rejection patterns.

Conclusions: Grading of rejection in cervical biopsies is reproducible and applicable to biopsies from different centers. Diagnosis of rejection may be improved by adding further histological lesions to the grading system; however, lesions require rigorous consensus definition.

FIGURE 1.

Study layout. The study was divided into 2 rounds of grading, based on 145 and 48 scanned slides, respectively. Five pathologists independently graded rejection according to the proposed grading scheme (no rejection, borderline changes, mild, moderate, and severe rejection). In the first round, the presence/absence of PVSI was also recorded. After the first round of grading, participants met virtually to discuss controversial cases and to identify histological lesions, which are currently not considered for a diagnosis of rejection, and, however, might be part of the spectrum of rejection. Two additional lesions (venous endothelial inflammation and apoptosis) were recorded as absent/present in the second round, together with the grading of rejection and the recording of PVSI. PVSI, perivascular stromal inflammation; VEI, venous endothelial inflammation.

FIGURE 2.

Histological lesions. A, Perivascular stromal inflammation: inflammatory infiltrates, dominated by lymphocytes, surrounding venules in the cervical stroma. Perivascular stromal inflammation was regarded as being present in this sample by 5 of 5 pathologists. B, Venous endothelial inflammation: inflammatory cells underneath the endothelium, lifting the endothelial cells (arrow). Venous endothelial inflammation was regarded as being present in this sample by 3 of 5 pathologists. C, Apoptosis: an apoptotic cell is seen in the basal layer of the surface squamous epithelium (arrowhead). Apoptosis was regarded as being present in this sample by 4 of 5 pathologists. (All hematoxylin and eosin–stained samples were originally scanned at ×40 magnification).

FIGURE 3.

Interrater agreement coefficients. As described in the Materials and Methods section, the interrater agreement coefficients displayed here were calculated using Krippendorff’s alpha coefficient. Both grading of rejection (based on the 5-tier grading scheme) and recording of PVSI were performed in both the first and second rounds. VEI and apoptosis were recorded in the second round, after the group discussion. PVSI, perivascular stromal inflammation; VEI, venous endothelial inflammation.

FIGURE 4.

Association of histological lesions with rejection. For this analysis, a gold-standard diagnosis was established for each parameter (rejection grade, presence/absence of VEI, PVSI, and apoptosis, respectively) in the following manner: For each pathologist, the mean of all pairwise interrater agreement coefficients was calculated. The pathologist with the highest mean interrater agreement score for a specific parameter served as the gold standard for that particular parameter. Please note that the numbers in each diagnostic group differ from the numbers in Table 1 (which represent the study lead’s judgment but not the gold standard). Groups were compared as follows: no rejection versus borderline; no rejection versus rejection (all); borderline versus rejection (all). All displayed P values were adjusted for multiple testing. A, Association of PVSI with rejection in the first round. B, Association of PVSI with rejection in the second round. Please note that 1 case was missed during grading by one of the participants; therefore, a total of n = 47. C, Association of VEI with rejection in the second round. D, Association of apoptosis with rejection in the second round. PVSI, perivascular stromal inflammation; VEI, venous endothelial inflammation.