Abstract: All studies were retrospective, and the majority reported consecutive sampling of cases. Sensitivity and specificity results were available from 38 studies involving 11,181 participants (3200 with invasive cancer, 1055 with borderline tumours and 6926 with benign tumours, determined by paraffin section as the reference standard). The median prevalence of malignancy was 29% (interquartile range (IQR) 23% to 36%, range 11% to 63%). We assessed test performance using two thresholds for the frozen section test. Firstly, we used a test threshold for frozen sections, defining positive test results as invasive cancer and negative test results as borderline and benign tumours. The average sensitivity was 90.0% (95% confidence interval (CI) 87.6% to 92.0%; with most studies typically reporting range of 71% to 100%), and average specificity was 99.5% (95% CI 99.2% to 99.7%; range 96% to 100%). Similarly, we analysed sensitivity and specificity using a second threshold for frozen section, where both invasive cancer and borderline tumours were considered test positive and benign cases were classified as negative. Average sensitivity was 96.5% (95% CI 95.5% to 97.3%; typical range 83% to 100%), and average specificity was 89.5% (95% CI 86.6% to 91.9%; typical range 58% to 99%). Results were available from the same 38 studies, including the subset of 3953 participants with a frozen section result of either borderline or invasive cancer, based on final diagnosis of malignancy. Studies with small numbers of disease-negative cases (borderline cases) had more variation in estimates of specificity. Average sensitivity was 94.0% (95% CI 92.0% to 95.5%; range 73% to 100%), and average specificity was 95.8% (95% CI 92.4% to 97.8%; typical range 81% to 100%). Our additional analyses showed that, if the frozen section showed a benign or invasive cancer, the final diagnosis would remain the same in, on average, 94% and 99% of cases, respectively. In cases where the frozen section diagnosis was a borderline tumour, on average 21% of the final diagnoses would turn out to be invasive cancer. In three studies, the same pathologist interpreted the index and reference standard tests, potentially causing bias. No studies reported blinding pathologists to index test results when reporting paraffin sections. In heterogeneity analyses, there were no statistically significant differences between studies with pathologists of different levels of expertise. In a hypothetical population of 1000 patients (290 with cancer and 80 with a borderline tumour), if a frozen section positive test result for invasive cancer alone was used to diagnose cancer, on average 261 women would have a correct diagnosis of a cancer, and 706 women would be correctly diagnosed without a cancer. However, 4 women would be incorrectly diagnosed with a cancer (false positive), and 29 with a cancer would be missed (false negative). If a frozen section result of either an invasive cancer or a borderline tumour was used as a positive test to diagnose cancer, on average 280 women would be correctly diagnosed with a cancer and 635 would be correctly diagnosed without. However, 75 women would be incorrectly diagnosed with a cancer and 10 women with a cancer would be missed. The largest discordance is within the reporting of frozen section borderline tumours. Investigation into factors leading to discordance within centres and standardisation of criteria for reporting borderline tumours may help improve accuracy. Some centres may choose to perform surgical staging in women with frozen section diagnosis of a borderline ovarian tumour to reduce the number of false positives. In their interpretation of this review, readers should evaluate results from studies most typical of their population of patients.

Plain-language summary: We included 38 studies (11,181 women), reporting three types of diagnoses from the frozen section test. 1. Cancer, which occurred in an average of 29% of women. 2. Borderline tumour, which occurred in 8% of women. 3. Benign mass. In a hypothetical group of 1000 patients where 290 have cancer and 80 have a borderline tumour, 261 women would receive a correct diagnosis of a cancer and 706 women would be correctly diagnosed without a cancer based on a frozen section result. However, 4 women would be incorrectly diagnosed as having a cancer where none existed (false positive), and 29 women with cancer would be missed and potentially need further treatment (false negative). If surgeons used a frozen section result of either a cancer or a borderline tumour to diagnose cancer, 280 women would be correctly diagnosed with a cancer and 635 women would be correctly diagnosed without a cancer. However, 75 women would be incorrectly diagnosed as having a cancer, and 10 women with cancer would be missed on the initial test and found to have a cancer after surgery. If the frozen section result reported the mass as benign or malignant, the final diagnosis would remain the same in, on average, 94% and 99% of the cases, respectively. In cases where the frozen section diagnosis was a borderline tumour, there is a chance that the final diagnosis would turn out to be a cancer in, on average, 21% of women. Where the frozen section diagnosis is a borderline tumour, the diagnosis is less accurate than for benign or malignant tumours. Surgeons may choose to perform additional surgery in this group of women at the time of their initial surgery in order to reduce the need for a second operation if the final diagnosis turns out to be a cancer, as it would on average in one out of five of these women.