Certain Melanomas Are Often Misdiagnosed

Pathologists face a greater likelihood of misinterpreting and misdiagnosing melanomas of moderate severity, according to a recent study.

Melanomas with the greatest risk of misinterpretation include moderate atypia, severe atypia or melanoma in situ, and pathologic state T1a (pT1a) early invasive melanoma.
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In this observer accuracy and reproducibility study, the skin biopsy cases of 240 participants were examined. Participants were grouped into sets of 36 or 48, and 187 pathologists were randomly assigned to diagnose the same set during 2 phases, with 8 months between each phase.

The researchers divided the pathologists’ diagnoses into 5 classes, ranging from more benign to most severe: I (nevus or mild atypia), II (moderate atypia), III (severe atypia or melanoma in situ), IV (pT1a early invasive melanoma), and V (pT1b or greater invasive melanoma).

Reproducibility was evaluated via intraobserver and interobserver concordance rates, and accuracy was determined by concordance with 3 reference diagnoses from a panel of experienced pathologists.

The pathologists, who were from 10 US states, interpreted a total of 8976 independent cases in phase 1 and again in phase 2, with an average of 10 different diagnostic terms used in each case.

Results showed that pathologists tended to give the same diagnosis in phase 2 as in phase 1 for more benign (class I) or most severe (class V). A total of 76.7% of class I diagnoses and 82.6% of class V diagnoses received the same diagnosis in both phases.

However, lower intraobserver reproducibility was seen among diagnoses for cases interpreted during phase 1 as having more moderate severity, with 35.2% of class II diagnoses, 59.5% of class III diagnoses, and 63.2% of class IV diagnoses receiving the same diagnosis in phase 2.

Average interobserver concordance rates were lower as well, but demonstrated similar trends, the researchers noted. Accuracy varied among classes, with highest accuracy among cases interpreted as more benign or very severe: I (92%), II (25%), III (40%), IV (43%), and V (72%).

The researchers estimated that, at a population level, 82.8% of melanocytic skin biopsy diagnoses would be verified if reviewed by a consensus reference panel of experienced pathologists, with 8.0% of cases overinterpreted by the initial pathologist and 9.2% underinterpreted.

“Diagnoses spanning moderately dysplastic nevi to early stage invasive melanoma were neither reproducible nor accurate in this large study of pathologists in the [United States],” the researchers concluded. “Efforts to improve clinical practice should include using a standardized classification system, acknowledging uncertainty in pathology reports, and developing tools such as molecular markers to support pathologists’ visual assessments.”

—Christina Vogt

Reference:

Elmore JG, Barnhill RL, Elder DE, et al. Pathologists’ diagnosis of invasive melanoma and melanocytic proliferations: observer accuracy and reproducibility study [published online June 28, 2017]. BMJ. doi:10.1136/bmj.j2813.