Accurate evaluation of PD-L1 status is critical for appropriate treatment strategy chosen in advanced NSCLC. Our findings indicate that the PD-L1 status showed heterogeneous between CNBs in one tumor, and the highest TPS revealed by one of the multiple CNBs was the most suitable score to reflect the PD-L1 status of matched resection specimen. The quantity of CNB required was correlated with different cutoff value set, such as 1% or 50% according to different treatment strategies.
The PD-L1 status of biopsies had been previously reported [1, 3, 7, 8, 10]. Some of the studies used the archival biopsies[3, 7, 8], while some studies were based on TMAs as surrogates of biopsy specimens[1, 10]. But, these materials (the archival biopsies and TMAs) were unsuitable for our study. This study focused on the heterogeneity of PD-L1 status between different CNBs in one tumor and their potential influence of PD-L1 evaluation in NSCLC. In this study, the actual surgical specimens were punctured for simulating CNB in vitro. Our design is most closely reflecting the actual procedure of core biopsy. It can obtain tissues in one tumor as much as possible, to satisfy the needs of study. The heterogeneity of PD-L1 status were showed between the CNBs from one tumor. It was observed in the cases with PD-L1 positive, regardless of PD-L1 high or low expression (Supplementary table 1), tumor size (Supplementary table 2) and histological subtypes (Supplementary table 3). The heterogeneity of PD-L1 status showed between the CNBs may be the main reason for the previous conflict results on using lung CNBs for PD-L1 evaluation.
In clinical practice, more than one tissue may be obtained during the percutaneous pulmonary biopsy. Pathologists and clinicians may be confused with which tissue could closely reflect the actual PD-L1 expression of the tumor. Our results suggested that the tissue with the highest TPS were able to better reflect the PD-L1 status of resection specimen. The coincident rates were 94.1% and 92.2% at the 1% and 50% cut-offs, respectively. This result was consistent with the Munari’s study. In Munari’s study, TMAs were used as surrogates of biopsy specimens. The maximum value appeared to better reflect PD-L1 expression on the whole sections, compared with mean, median and minimum values of biopsy. Our study was based on real punctured core tissue collected from the resection specimens to simulate the CNB, and included more values (weighted average TPS, TPS of the longest biopsy specimen and TPS of the biopsy with most tumor volume). So, this result should be more objective and scientific.
The heterogeneity of PD-L1 expression is variable in its scale and extent, so it’s hard to accurate assess PD-L1 expression. Several studies have tried to quantify how many biopsy specimens of a NSCLC are required to provide accurate coverage of PD-L1 expression within a tumor[3, 10], most concluded that more biopsies were likely to provide greater accuracy. Haragan’s study showed that extensive sampling reduced the inaccuracy, but cannot eliminate it. In current study, the heterogeneity was found between CNBs obtained from the same surgical resected specimen. But more tissues did not improve the predictive accuracy, when the cutoff was set to 1%. The probability of accuracy was consistently more than 90% (Table 3). While in patients with PD-L1 high expression whose TPS ≥ 50%, the accuracy was associated with the quality of biopsy. The coincidence rare was only 71.4%, when the biopsy density was less than 0.75 core/cm, and increase to 97.3% when the biopsy density was more than 1 core/cm (Table 3). Patients with advanced NSCLC should be treated with pembrolizumab alone as first-line therapy if PD-L1 TPS ≥ 50%. Results of the current study suggested that insufficient quantity of CNB tissue may lead to underestimate of accurate PD-L1 status, which will allow more patients to benefit from immunotherapy. But the likelihood of getting more tissue may increase the risk of pneumothorax and hemorrhage. Our results showed that the tissues needed for accurate evaluation of PD-L1 status was correlated with the given cutoffs. According to different treatment purposes, if the concerned cutoff value is 1%, a few biopsies tissue could be enough. Nevertheless, if the concerned cutoff value is 50%, insufficient biopsies may lead to underestimation of PD-L1 status. It will provide great use for pathologists and oncologists in accurate evaluation of PD-L1 status of NSCLC patients.
Anti-PD-1/PD-L1 therapy has been recommended for the patients with unresectable NSCLC. We simulated real CNBs using resected NSCLC specimens in this study. The intratumoral heterogeneity of PD-L1 expression is ill-understood. Even detailed and extensive study in large series of tumors cases fails to reveal any particular pattern of this heterogeneity. Therefore, we suggest that there is no difference between the unresectable and resectable NSCLC in the intratumoral heterogeneity of PD-L1 expression.
In conclusion, the inter-heterogeneity of PD-L1 status was found in the biopsies from the same tumor. The highest TPS of multiple biopsies made the most sense in the evaluation of the PD-L1 status. The quantity of core needle biopsies needed for accurate evaluation of PD-L1 status was correlated with the concerned cutoffs.