Immunohistochemistry and immunofluorescence utilization audit by subspecialty in an academic setting: A step toward stewardship

There are immunohistochemistry (IHC) and immunofluorescence (IF) panels described in the literature and established by personal and institutional experiences that are in common use by pathologists in their daily practice. Stewardship is a difficult discussion because IHC utilization is influenced by many factors including the pathologist's experience, background, practice setting, personal bias, and medicolegal culture. We developed the methodology to audit the IHC/IF utilization in our academic subspecialty practice. We aim to share this methodology and to provide our data that can be used for consideration by other subspecialized academic practices. This analysis included a total of 63,157 specimens that were accessioned during 2022, representing 38,612 cases. The likelihood of ordering IHC/IF ranged from 1 % (in genitourinary pathology) to 59 % (in renal pathology). The average percentage of specimens with IHC/IF was 21 % for the entire practice. In cases where IHC/IF was ordered, the number of stained slides averaged 4.9 per specimen for the entire practice. The number of IHC/IF slides per specimen ranged from 1.9 (in gastrointestinal pathology) to 12.2 (in renal pathology). The highest number of antibodies ordered for a single specimen by subspecialty ranged from 11 (in cardiac pathology) to 63 (in dermatopathology). Renal pathology was the only subspecialty that had an average number of IHC/IF slides that was statistically significantly different from all other subspecialties. We described the various patterns of utilization by subspecialty and rationalized their subtle differences. We also analyzed the types of cases that exceeded the reimbursement limits set by the Centers for Medicare and Medicaid Services (CMS).

The utilization and utility of immunostains in body fluid cytology

BACKGROUND

Body fluid cytology (BFC) is an important tool in the diagnosis and staging of malignancy and is aided by the judicious use of immunohistochemistry (IHC). The aim of this study was to determine the usage rates of IHC stains in BFC, their type and indications, and their diagnostic impact. We also attempted to estimate the optimal rate of IHC use in BFC by comparing the entire laboratory's and each individual cytopathologist's IHC use rates with their respective indeterminate and malignant diagnosis rates.

METHODS

We conducted a retrospective study of IHC stain use in BFC during a 5.5-year interval (2013-2018) and determined the laboratory's and each individual cytopathologist's IHC usage patterns according to the final diagnosis, site, and indications for their use.

RESULTS

A total of 477 out of 4144 (11.5%) BFC cases had 2128 individual immunostains performed, with an average of 4.5 immunostains per case. Individual cytopathologists used IHC stains on 6.7% to 22% of their BFC cases. Pathologists with higher rates of IHC stain use than the laboratory's mean were less experienced and had higher rates of indeterminate but not of malignant diagnoses. The most common indication for the use of IHC stains was differentiating mesothelial from malignant cells. MOC31, calretinin, Ber-EP4, CD68, and D2-40 were the most commonly used of the 67 different IHC stains used in BFC.

CONCLUSIONS

The laboratory's mean may represent the optimal IHC use rate, as higher IHC use rates did not lead to more diagnostic certainty or higher pickup rates of malignant cells.

Differences in immunohistochemistry utilization by general and breast subspecialty pathologists at a large academic institution

OBJECTIVES

Immunohistochemistry (IHC) can be a useful adjunct in diagnostic breast pathology, but best practices have not been clearly established. We sought to compare the patterns of p63 utilization between general pathologists (GP) and subspecialized breast pathologists (BP), analyze diagnostic discrepancy rates, and identify types of lesions requiring immunohistochemistry.

METHODS

The pathology database was searched over 6-year period to identify breast needle core biopsy cases utilizing p63 and subsequent excision results.

RESULTS

P63 was ordered more frequently by BP (2.3% of cores) compared to GP (1.1% of cores, p = 0.0005). The most frequent utilization of p63 by GP for benign lesions (44.0%) followed by invasive carcinomas (36.0%) while BP most frequently ordered p63 on invasive carcinomas (49.5%) and DCIS (26.6%).

CONCLUSIONS

While IHC use may be thought to be most helpful to those with less experience or knowledge in breast pathology, these results suggest that utilization is increased with subspecialty training.

Impact of the Pathologist on Prostate Biopsy Diagnosis and Immunohistochemical Stain Usage Within a Single Institution

OBJECTIVES

To determine whether pathologists in a tertiary care institution vary in diagnosis and immunohistochemical stain usage in prostate biopsy specimens.

METHODS

Men who underwent prostate needle biopsies between 2008 and 2013 were included.

RESULTS

In total, 1,777 prostate biopsy specimens diagnosed by nine pathologists showed variation in diagnostic reporting (atypical small acinar proliferation, 2.0%-8.0%; high-grade prostatic intraepithelial neoplasia, 2.0%-8.5%; nonneoplastic, 30.2%-48.3%; adenocarcinoma, 46.2%-55.3%; P < .001). Variation in Gleason scoring was observed (P < .001), with the 4 + 3 = 7 category having the greatest variability (6.9%-30.3%). A blinded review from the most outlying pathologist in this category revealed 45% grading discrepancies. The mean number of immunostains performed per case (0.3-1.2) differed between pathologists (P < .001), and one pathologist used immunostains at twice the rate of the remaining cohort.

CONCLUSIONS

Case pathologist significantly affects prostate biopsy diagnosis and immunohistochemical workup. We recommend evaluation for outlying practice patterns to provide consistent and efficient patient care.

Immunohistochemistry in the workup of prostate biopsies: Frequency, variation and appropriateness of use among pathologists practicing at an academic center

OBJECTIVES

We studied the frequency, inter-pathologist variation, appropriateness and utility of immunohistochemistry (IHC) performed on prostate biopsies (PB) to determine the significance of foci of suspicious glands/atypical small acinar proliferations (ASAP).

METHODS

We calculated the rate of IHC use and diagnostic rate of ASAP and adenocarcinoma in PB from 01/01/2008 to 06/30/2015 for individual pathologists working in a tertiary academic institution, and correlated them with the pathologists' experience, subspecialization and PB volume with the aim of determining the interpathologist variation and appropriateness of use of IHC according to recently published recommendations, and the usefulness of IHC to resolve foci of ASAP as either benign or adenocarcinoma.

RESULTS

IHC was used in 966/2652 (36.4%, 95% CI 33.4-39.4%) PB cases and 1915 of 16,359 (11.7%, 95% CI 11.2%-12.2%) of PB blocks and allowed definitive diagnosis of either benign or malignant in 75.8% (95% CI 73.9-77.7%) of blocks. By pathologist, IHC use rates varied more than twofold (22.8-50.5%); higher use was found for pathologists with genitourinary pathology specialization, higher PB volume and more experience, and correlated with higher rates of both ASAP and adenocarcinoma diagnoses. The use of IHC stains was considered appropriate in 822/966 (85.1%, 95% CI 82.9-87.4%) cases.

CONCLUSIONS

Despite the fact that the use of IHC stains was considered useful and deemed appropriate in the majority of cases, it showed wide variation between pathologists, suggesting monitoring of IHC use rates may be useful to standardize its use.

Immunohistochemistry Is Rarely Justified for the Diagnosis of Viral Infections

OBJECTIVES

To determine the utility of immunohistochemistry (IHC) for the diagnosis of viral infections in surgical pathology specimens lacking characteristic viral cytopathic effects.

METHODS

Five years of cases at an academic medical center were reviewed for the use of IHC to detect cytomegalovirus (CMV), herpes simplex virus 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), adenovirus, or polyomavirus (ie, BK or JC).

RESULTS

In total, 1,636 viral IHC stains were ordered on 1,099 specimens from 957 cases. Altogether, 134 (8.2%) stains were positive, including 59 (7.9%) of 749 for CMV, 34 (8.9%) of 384 for HSV-1 and HSV-2, 16 (11.5%) of 139 for VZV, three (1.4%) of 210 for adenovirus, and 22 (14.3%) of 154 for polyomavirus. In 101 (75.4%) of 134 cases, viral cytopathic effect (VCPE) was readily identifiable on H&E slides. No significant changes in clinical care occurred in any of the cases without definitive VCPE that had positive staining cells on IHC.

CONCLUSIONS

These findings suggest that IHC for viral infections without a high degree of clinical or histologic suspicion is unnecessary in most cases.

Use of individual containers for prostate biopsy samples: Do we gain diagnostic performance?

OBJECTIVE

Prostate cores from transrectal biopsies are usually sent in separate vials for pathological processing. Although this is a common practice, there are controversial studies on its usefulness. We wanted to compare the rate of prostate cancer diagnosis between processing samples in 2 containers and processing them in individual containers to see if there are differences. Our secondary objective was to check the rate of diagnosis of various tumour subtypes in each of the 2 groups.

MATERIAL AND METHODS

A retrospective observational study was conducted of 2,601 cases of prostate biopsies. Ten cores were extracted in each biopsy. We divided the sample into 2 groups: biopsies sent in 2 containers to the department of pathology (left and right lobes) or sent in 10 (one for each cylinder), according to the different criteria used in our centre in the past. We then classified the cases according to the absence of neoplasia, insignificant tumour (involvement of just 1 cylinder, <5%, Gleason score<7), Gleason 6 or Gleason≥7. A bivariate statistical analysis was performed using the chi-squared test.

RESULTS

A total of 1,777 participants were included in the 2-container group, and 824 were included in the 10-container group. We diagnosed a rate of 32.4% of cancers in the 2-container group and 40% in the 10-container group, a difference that was statistically significant (P<.001). The insignificant carcinomas were diagnosed more often in the 2-container group than in the 10-container group (6.4% vs. 4.3%, respectively; P=.03). Samples with a Gleason score of 6 were diagnosed more often in the 10-container group than in the 2-container group (11.9% vs. 8.1%, respectively; P=.002). The same occurred with the Gleason score≥7 (23.8% in the 10-container group vs. 17.9% in the 2-container group; P<.001).

CONCLUSIONS

We diagnosed more prostate cancers when sending biopsied cores in individual containers. Once the procedure was conducted, we also observed in our series a reduction in the diagnoses of insignificant carcinoma to the detriment of an increased diagnosis of not insignificant carcinomas.