Diagnosis of serous tubal intraepithelial carcinoma based on morphologic and immunohistochemical features: a reproducibility study

Abstract

There is compelling evidence that serous tubal intraepithelial carcinoma (STIC) is a precursor of high-grade serous ovarian carcinoma. Large-scale studies are now required to determine its biological significance and clinical implication. Before conducting these studies, a reproducible classification for STIC is needed, and that is the goal of this study. This study involved 6 gynecologic pathologists from 4 academic institutions and 3 independent rounds of review. In round 1, sixty-seven lesions ranging from normal, atypical, to STICs were classified by 5 pathologists on the basis of predetermined morphologic criteria. Interobserver agreement for the diagnosis of STIC versus not STIC was fair [κ = 0.39; 95% confidence interval (CI) 0.26, 0.52], and intraobserver reproducibility ranged from fair to moderate on the basis of percentage agreement and κ. Round 2 involved testing revised criteria that incorporated morphology and immunohistochemistry (IHC) for p53 protein expression and Ki-67 labeling in 10 sets by 3 of the pathologists. The result was an improvement in interobserver agreement for the classification of STIC (κ = 0.62; 95% CI 0.18, 1.00). An algorithm was then created combining morphology and IHC for p53 and Ki-67, and reproducibility was assessed as part of round 3. In 37 lesions reviewed by 6 pathologists, substantial agreement for STIC versus no STIC was observed (κ = 0.73; 95% CI 0.58, 0.86). In conclusion, we have developed reproducible criteria for the diagnosis of STIC that incorporate morphologic and IHC markers for p53 and Ki-67. The algorithm we propose is expected to help standardize the classification of STIC for future studies.

FIGURE 1

A flow chart describing the process that was undertaken to assess reproducibility of STIC.

FIGURE 2

Pathologic classification of fallopian tube lesions for rounds 1 to 3. A, Morphologic classification of fallopian tube lesions by each pathologist at 2 time points in round 1. B, Morphologic and immunohistochemical classification of fallopian tube lesions by each pathologist at 1 time point in round 2. C, Morphologic and immunohistochemical classification of fallopian tube lesions by each pathologist at 1 time point in round 3 based on the algorithm described in Figure 3. STIL indicates serous tubal intraepithelial lesion, STIC for serous tubal intraepithelial carcinoma and N/R indicates for normal/reactive. p53 signature is characterized by a strip of normal-appearing fallopian tube epithelium, at least 12 cells in length, which strongly expresses p53.

FIGURE 3

Algorithm for the diagnosis of STIC. Foci showing a Ki-67 labeling index >10% are considered Ki-67 high, whereas a Ki-67 labeling index of <10% is considered low. Diffuse moderate-to-strong expression of p53 in >75% of at least 12 epithelial cells (with or without intervening ciliated cells) or complete absence of staining has been shown to be compatible with a TP53 mutation either missense or nonsense (p53 MUT versus p53WT pattern in algorithm).

FIGURE 4

Final diagnosis of STIC by all 6 observers. Normal epithelium for comparison is present in the upper left corner. A, Morphologic designation of unequivocal STIC by all 6 observers. The epithelium is slightly stratified with loss of polarity and nuclear molding. A longitudinal cleft within the epithelium is present at the center of the photograph. The nuclei are enlarged with prominent nucleoli, and the nuclearto-cytoplasmic ratios are increased. B, The p53 immunostain was interpreted as “compatible with a TP53 mutation” by all 6 observers. C, High Ki-67 labeling index by all 6 observers.

FIGURE 5

Final diagnosis of STIL by all 6 observers. Normal epithelium for comparison is present in the lower left corner. A, Morphologic designation of suspicious for STIC by all 6 observers. The epithelium shows a suggestion of nuclear molding. Some nuclei are enlarged, rounded, and hyperchromatic; however, the overall morphologic features were not interpreted as sufficient for a morphologic designation of unequivocal STIC. B, The p53 immunostain was interpreted as “compatible with a TP53 mutation” by all 6 observers. C, Low-Ki-67 labeling index by all 6 observers.

FIGURE 6

Final diagnosis of normal/reactive by all 6 observers. Normal epithelium for comparison is present in the lower right corner. A, Morphologic designations of suspicious for STIC by 2 observers and not suspicious for STIC by 4 observers. The epithelium is slightly stratified, and the nuclei are questionably hyperchromatic. B, The p53 immunostain was interpreted as “NOT compatible with a TP53 mutation” by all 6 observers. C, Low-Ki-67 labeling index by all 6 observers.

FIGURE 7

Final diagnosis of p53 signature by all 6 observers. A, Morphologic designation of not suspicious for STIC by all 6 observers. Although no obviously ciliated cells are evident within the epithelium, no appreciable atypia is identified. B, The p53 immunostain was interpreted as “compatible with a TP53 mutation” by all 6 observers. C, Low-Ki-67 labeling index within the same segment showing a positive p53 pattern in (B) by all 6 observers.

FIGURE 8

Final diagnoses of STIC by 4 observers and STIL by 2 observers. A, Morphologic designations of unequivocal for STIC by 3 observers and suspicious for STIC by 3 observers. The epithelium is slightly stratified, and the nuclei are questionably enlarged and hyperchromatic. B, The p53 immunostain was interpreted as “compatible with a TP53 mutation” by all 6 observers. C, High Ki-67 labeling index by 4 observers and low-Ki-67 labeling index by 2 observers.