PD-L1 expression and tumor-infiltrating T lymphocytes as prognostic factors in canine mammary tumors.

Background Immune checkpoint-inhibitors targeting the PD-1/PD-L1 system are FDA approved in microsatellite instable (MSI) or mismatch repair deficient (dMMR) colorectal cancer (CRC). PD-L1 expression is tightly linked to features connected to immune checkpoint inhibitor response, but studies on large subsets of cancers analyzing the correlation between different status of MSI/dMMR, tumor infiltrating lymphocytes and PD-L1 expression are still lacking. Methods More than 1800 CRC were analyzed for PD-L1 by immunohistochemistry in a tissue microarray format. Data were compared to MMR, the number of intratumoral CD8+ cytotoxic T-cells, and adverse clinico-pathological parameters. Different cutoff levels for defining PD-L1 positivity in tumor cells (1%, 5%, 10%, and 50%) yielded comparable results. Results At a cutoff level of 5%, PD-L1 positivity was seen in 5.1% of tumors. PD-L1 was more often positive in dMMR (18.6%) than in MMR proficient (pMMR) cancers (4.1%; p < 0.0001). The number of intratumoral CD8+ lymphocytes was strikingly higher in PD-L1 positive (939.5 ± 118.2) than in PD-L1 negative cancers (310.5 ± 24.8). A higher number of intratumoral CD8+ lymphocytes was found in dMMR CRC (PD-L1 positive: 1999.7 ± 322.0; PD-L1 negative: 398.6 ± 128.0; p < 0.0001) compared to pMMR CRC (PD-L1 positive: 793.2 ± 124.8; PD-L1 negative: 297.2 ± 24.2; p < 0.0001). In dMMR and pMMR CRC, PD-L1 expression in tumor cells was unrelated to tumor stage, lymph node status or lymphatic/venous invasion. PD-L1 positivity in tumor associated immune cells was seen in 47.5% of cases and was significantly linked to high numbers of tumor infiltrating CD8+, low tumor stage, and absence of lymph node metastasis and lymphatic/venous invasion (p < 0.0001 each). Conclusion The data support the previously suggested fact that PD-L1 expression in tumor cells is driven by extensive cytotoxic T-cell infiltration in highly immunogenic dMMR and pMMR CRC. Frequent and intense PD-L1 expression in tumor cells of dMMR CRC may contribute to the high response rates of dMMR CRC to immune checkpoint-inhibitors.

424 Background: Programmed death-1 (PD-1) receptor negatively regulates T cell-mediated responses.PD-1 ligand (PD-L1) is aberrantly expressed in clear cell renal cell carcinoma (ccRCC) and is associated with worse prognosis. Levels of PD-L1 expressions in non-ccRCC and its association with clinicopathological features and survival are unknown. Methods: Formalin-fixed paraffin-embedded (FFPE) specimens were obtained from 97 patients with chromophobe (CHR), papillary (PAP), translocation Xp11.2 (TrL) RCC and oncoytoma (ONC) and were included in the analysis. PD-L1 expression was evaluated by immunohistochemistry using a mouse monoclonal anti-PD-L1 antibody (405.9A11). The assay was validated using FFPE cell line controls known to be positive or negative for PD-L1 expression by flow cytometry. PD-L1 tumor positivity (PD-L1+) was defined as ≥5% tumor cell membrane staining. For PD-L1 expression in immune cells, a combined score based on the intensity of infiltrate and percentage of positive cells was used. Baseline characteristics including stage/grade, and survival data were collected. Comparisons between PD-L1 expression and clinicopathological features were evaluated using chisq or wilcoxon rank sum tests. Cox model tests for association of PD-L1 expression with OS in univariate and multivariable analysis. Results: Among 97 patients, 12 (12.4%) were considered PD-L1+ in tumor cells: 2/36 (5%) of CHR RCC, 5/50 (10%) of PAP RCC, 3/7 (43%) of TrL RCC, and 2/4 (50%) of ONC. PD-L1 positivity in tumor cells was significantly associated with higher stage (p=0.026) and grade (p=0.046), as well as lower OS on univariate (p=0.02) but not multivariate analysis (p=0.29). On the other hand, PD-L1 positivity by immune cells was observed in 50 (51.5%) patients: 13/36 (36%) of CHR RCC, 30/50 (60%) of PAP RCC, 6/7 (86%) of TrL RCC, and 1/4 (25%) of ONC. PD-L1 positivity in immune cells did not correlate with stage (p=0.7), grade (p=0.1) or OS (p=0.8). Conclusions: PD-L1 expression is variable in non-ccRCC and depends on histology and tumor vs. immune cells scoring. Only PD-L1 positivity in tumors cells was associated with aggressive features. Patients with non-ccRCC should not be automatically excluded from trials of agents that target the PD-1/PD-L1 pathway.

BackgroundProgrammed death-ligand 1 (PD-L1) was the first identified ligand of programmed death-1 (PD-1). PD-1/PD-L1 interactions inhibit T cell-mediated immune responses, limit cytokine production, and promote tumor immune escape. Recently, many studies have investigated the prognostic value of PD-L1 expression in patients with melanoma. However, the results of these analyses remain a subject of debate. We have therefore carried out a meta-analysis to identify the prognostic role of PD-L1 in melanoma.MethodsA thorough medical literature search was performed in the databases PubMed, Web of Science, and Embase until October 2019. The pooled hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated to evaluate the correlation between PD-L1 overexpression and prognosis. Publication bias was evaluated using Begg’s test and Egger’s test.ResultsThirteen articles with 1062 enrolled patients were included in this meta-analysis. High PD-L1 expression did not correlate with overall survival (OS) (HR = 0.93, 95% CI 0.57–1.52, P = 0.781) or progression-free survival (PFS) (HR = 0.82, 95% CI 0.43–1.54, P = 0.535). However, PD-L1 overexpression correlated with the absence of lymph node (LN) metastasis (OR = 0.46, 95% CI 0.22–0.95, P = 0.036). Further, there was no significant relationship between PD-L1 expression and sex (OR = 1.29, 95% CI 0.90–1.84, P = 0.159), age (OR = 0.90, 95% CI 0.51–1.57, P = 0.708), or Eastern Cooperative Oncology Group Performance Status (OR = 0.55, 95% CI 0.06–4.83, P = 0.592).ConclusionsThis meta-analysis suggested that PD-L1 expression did not predict an inferior prognosis in patients with melanoma. However, high PD-L1 expression was associated with absence of LN metastasis in such patients.

183 Background: The phase 3 COMBI-v study (NCT01597908) showed that D+T significantly improved outcomes vs vemurafenib in pts with BRAF V600E/K–mutant MM. Checkpoint inhibitors also provide clinical benefit in some pts with MM. To date, characterization of markers associated with response to anti–PD-1 therapy has identified positive associations with PD-L1 expression and immune cell infiltration. Here we describe expression of PD-L1 and the T-cell marker CD8 in tumor samples from pts randomized to receive D+T in COMBI-v and associations with clinical outcomes. Methods: Biopsies from 74 of 352 D+T pts (21%) in COMBI-v were assessed for expression of PD-L1 (PD-L1 IHC 22C3 pharmDx assay; Dako) and CD8 (anti-CD8 antibody, clone C8/144B; Dako). PD-L1 positivity was determined as a percentage of stained tumor cells and MEL score (staining on both tumor and mononuclear inflammatory cells; 0 or 1 [negative]: &lt; 1% staining; 2-5 [positive]: ≥ 1% staining; Daud et al. J Clin Oncol. 2016). Results: Of 74 pts analyzed, 54 (73%) had PD-L1–positive tumors, and the largest MEL score subgroup was 2 (45%). A significant association ( P &lt; .0001) was observed between PD-L1 and CD8 expression. Overall response rate, tumor shrinkage, progression-free survival, overall survival (OS), and duration of response with D+T were not associated with PD-L1 (MEL score of ≥ 2) or CD8 positivity. However, a significant association ( P = .04) with improved OS was observed in tumors with high PD-L1 expression (≥ 20% of cells PD-L1 positive), and a trend ( P = .06) was seen in pts with a MEL score of ≥ 3. Among PD-L1–negative pts, improved OS was seen in those with high CD8 positivity ( P = .03), particularly in the stromal compartment. Conclusions: These data, representing PD-L1 and CD8 expression profiles for a BRAF-mutant MM population in the context of outcomes following D+T, showed that clinical benefit was maintained regardless of immune phenotype. The results also suggest that an immune component has an impact on outcomes following targeted therapy. Clinical trial information: NCT01597908.

9527 Background: The phase 3 COMBI-v study (NCT01597908) showed that D+T significantly improved outcomes vs vemurafenib in pts with BRAFV600E/K–mutant MM. Checkpoint inhibitors also provide clinical benefit in some pts with MM. To date, characterization of markers associated with response to anti–PD-1 therapy has identified positive associations with PD-L1 expression and immune cell infiltration. Here we describe expression of PD-L1 and the T-cell marker CD8 in tumor samples from pts randomized to receive D+T in COMBI-v and associations with clinical outcomes. Methods: Biopsies from 74 of 352 D+T pts (21%) in COMBI-v were assessed for expression of PD-L1 (PD-L1 IHC 22C3 pharmDx assay; Dako) and CD8 (anti-CD8 antibody, clone C8/144B; Dako). PD-L1 positivity was determined as a percentage of stained tumor cells and MEL score (staining on both tumor and mononuclear inflammatory cells; 0 or 1 [negative]: &lt; 1% staining; 2-5 [positive]: ≥ 1% staining; Daud et al. J Clin Oncol. 2016). Results: Of 74 pts analyzed, 54 (73%) had PD-L1–positive tumors, and the largest MEL score subgroup was 2 (45%). A significant association ( P &lt; .0001) was observed between PD-L1 and CD8 expression. Overall response rate, tumor shrinkage, progression-free survival, overall survival (OS), and duration of response with D+T were not associated with PD-L1 (MEL score of ≥ 2) or CD8 positivity. However, a significant association ( P = .04) with improved OS was observed in tumors with high PD-L1 expression (≥ 20% of cells PD-L1 positive), and a trend ( P = .06) was seen in pts with a MEL score of ≥ 3. Among PD-L1–negative pts, improved OS was seen in those with high CD8 positivity ( P = .03), particularly in the stromal compartment. Conclusions: These data, representing PD-L1 and CD8 expression profiles for a BRAF-mutant mm population in the context of outcomes following D+T, showed that clinical benefit was maintained regardless of immune phenotype. The results also suggest that an immune component has an impact on outcomes following targeted therapy. Clinical trial information: NCT01597908.

Immune checkpoint blockade therapy targeting programmed death (PD)-1 or PD-ligand 1 (L1) has shown promising results in renal cell carcinoma (RCC);however, the prognostic implications and clinicopathological features of PD-L1 and PD-L2 expression in RCC remain unclear. PD-L1 and PD-L2 expression was immunohistochemically evaluated in 425 resected RCCs of variable histologic subtypes and analyzed according to the clinicopathological status and oncogenic proteins status. PD-L1 expression was observed in 9.4 % with no difference between histologic subtypes, but PD-L2 was observed in 49.6 % with highest frequency in papillary RCC (PRCC) (P<0.001). In clear cell RCC (CCRCC), PD-L1 expression was associated with adverse features,including higher nuclear grade, necrosis, sarcomatoid transformation, c-MET expression (all, P<0.001) and VEGF expression (P = 0.002), whereas PD-L2 expression was related with c-MET and VEGF expression (P = 0.008 and P<0.001). In PRCC, positive correlations between PD-L1 and EGFR expression (P = 0.007) or between PDL2 and VEGF expression (P<0.001) were observed. In CCRCC, PD-L1 and PD-L2 positivity were significantly associated with shorter progression-free survival (P<0.001; P = 0.033) and cancer-specific survival (P<0.001; P = 0.010), but not in PRCC. PD-L1 and PD-L2 expression predict poor prognosis in CCRCC. Thus, PD-1/PD-L pathway-targeted immunotherapy may be useful for treatment of patients with CCRCC.

Background: PD-1 blockade has emerged as an effective treatment for a subset of cancer patients. Studies have shown that PD-L1 expression is associated with likelihood of response to PD-1 blockade. In order to select the right breast cancer patient for immunotherapy, characterization of the immune landscape of breast tumors is required. Therefore, we assessed PD-L1 expression and tumor-infiltrating lymphocytes (TILs) in different breast tumor subtypes and the link with prognosis. We also sequenced a panel of genes to assess the mutational load in triple negative tumors (TNBC) and investigate the association with PD-L1 positive TILs. Material and methods: We analyzed 438 tumor samples from breast cancer patients of all ages treated between 1986 and 2007 with surgery, with or without adjuvant therapy. PD-L1 was stained using whole slide specimens (E1L3N® antibody) after methodological validation. Pathologists quantified TILs based on International TILs Working Group recommendations and scored PD-L1 based on the percentage of positive (tumor and/or immune) cells; as negative if 0%, positive if ≥1%, and high if &amp;gt;50%. Mutational load was assessed based on DNA kinome sequencing. Associations were measured by Cox/logistic regression model, including pathological variables. Multiplex imaging of 20 immune-infiltrated areas from four ER negative tumors were performed using the Vectra® system based on immunofluorescence staining panel of: CD4, CD68, CD8, FOXP3 and PD-L1. Results: PD-L1 expression and TILs were higher in ductal (compared with lobular), high grade and estrogen receptor (ER)-negative tumors (p&amp;lt;0.001). TILs (density ≥5%) were significantly associated with worse distant metastasis-free survival (DMFS) only in ER-positive tumors (n=204): HR=2.72; 95%CI: 1.07-6.94. PD-L1 positivity (≥1%) followed the same trend: HR=1.66; 95%CI: 0.87-3.15. However, in ER-negative tumors (n=171), high PD-L1 expression (&amp;gt;50%) was significantly associated with better DMFS: HR=0.51; 95%CI: 0.27-0.98. TNBC with high PD-L1 expression of TILs (&amp;gt;50%) showed an association with increased mutation load (p=0.019) and a trend for better DMFS (HR=0.41; 95%CI: 0.16-1.04) compared with tumors lacking TILs. Further characterization of PD-L1 positivity in the immune-infiltrated cells was conducted by a multiplex imaging analysis. Preliminary results indicated that PD-L1 is expressed in CD68+, CD4+, FOXP3+ and CD8+ immune-cells. Conclusion: Our findings suggest that PD-L1 positive TILs are associated with worse prognosis in ER-positive breast cancer and with better outcome in ER-negative group. In TNBC, high mutational load correlates with high PD-L1 positive TILs. Citation Format: Marcelo Sobral-Leite, Koen Van de Vijver, Magali Michaut, Hugo M. Horlings, Tesa M. Severson, Philip C. Schouten, Rianne van der Linden, Kelly Kersten, Anna Marie Mulligan, Nayana Weerasooriya, Joyce Sanders, Ashley Cimino-Mathews, Dennis Peters, Gerrit K. Hooijer, Erik Hooijberg, Annegien Broeks, Rene Bernards, Sabine Linn, Irene L. Andrulis, Marc J. van de Vijver, Lodewyk F. Wessels, Marleen Kok, Karin E. de Visser, Marjanka K. Schmidt. PD-L1 positive tumor-infiltrating lymphocytes and mutational load in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 575. doi:10.1158/1538-7445.AM2017-575

Programmed cell death 1 (PD-1) and its ligand (PD-L1) are key physiologic suppressors of the cytotoxic immune reaction. However, to date, the combination of PD1/PD-L1 expression and tumor-infiltrating lymphocytes (TILs) and antigen-presenting cells has been only minimally reported in breast carcinoma, in particular in relation to HER2-positive cases. The goal of this study was to evaluate both cellular tumoral immune reaction and PD-L1/PD1 distribution in HER2-positive cases, as well as any associations with clinical outcome using conventional chemotherapy combined with HER2 blocking. Multicolor immunohistochemical multiplex assays simultaneously demonstrating PD1, PD-L1, and CD8 or PD-L1, CD3, and CD163 were performed on tissue microarrays (TMA) representing 216 pretreatment cases of HER2-positive invasive breast carcinoma. PD-L1 expression was identified in 38 cases (18%), including 12 cases (6%) with PD-L1 labeling of tumor cells and 26 cases (12%) with PD-L1 labeling of immune cells only. Ten of 12 cases with PD-L1 staining of tumor cells showed staining of associated immune cells as well. With this assay method, PD1 was detectable in many fewer cases (6 cases or 3%). PD-L1 expression was positively associated with high Nottingham grade, negative ER and PR, the absence of lymph node metastasis, and high levels of CD8+ cells. The overall survival by univariate analysis was positively associated with lower tumor stage, the absence of lymph node metastasis, PD-L1 expression, and high levels of CD8+ cells. Therefore, our data suggest cytotoxic immune reaction mediated by CD8-positive T cells and PD-L1 expression may predict a better outcome in patients with HER2-positive breast carcinoma managed with conventional chemotherapy and HER2-blocking therapy. These findings recommend clinical trials utilizing checkpoint blocking immunotherapy in some form for HER2-positive breast cancer.

Background: In neoadjuvant setting, PD-1 inhibitors have shown significantly higher pathological responses in patients (pts) with early-stage triple-negative breast cancer (TNBC) irrespective of PD-L1 status. However, durable responses are less common in estrogen receptor-positive (ER+) pts. Most breast cancer (BC) clinical trials of PD-1 inhibitors have thus far focused on PD-L1 expression for patient eligibility. The alternative PD-1 ligand, PD-L2, with reported ~4-fold greater affinity for PD-1, has been largely understudied. We recently reported that high cancer cell protein levels of PD-L2 in pts with treatment-naïve ER+ BC was an independent predictor of shorter progression-free survival. PD-L2 expression was significantly high in ER- group as well, however, given the low numbers of ER- pts, the study was not powered enough to determine the correlation of PD-L2 with PFS in the ER- subgroup. These findings suggest that PD-L2 has an important role in BC and combined PD-L1/PD-L2 status may help improve BC pt selection for PD-1 inhibitors. We therefore initiated efforts to determine baseline expression patterns of PD-L1 and PD-L2 in BC. Methods: PD-L1 and PD-L2 protein levels in cancer cells and tumor-infiltrating immune cells were prospectively analyzed by immunohistochemistry (IHC) using validated antibodies in diagnostic core biopsies of 31 consecutive pts diagnosed with localized or locoregional ER+/HER2- BC or TNBC. Percent positivity of PD-L1 and PD-L2 in cancer cells and immune cells was determined by our breast pathologist. Detectable PD-L1 or PD-L2 expression in ≥1% of cancer cells or stromal immune cells was considered positive. Spearman correlation and Wilcoxon paired analyses were used to measure and correlate PD-L1 and PD-L2 protein expression in cancer and immune cells. Results: There was no significant correlation between PD-L1 and PD-L2 expression, neither across all cases (N=31), nor within ER+ (N=22) or TNBC (N=9) cases. However, PD-L1 and PD-L2 expression patterns in BC differed in several ways. PD-L1-positivity in immune cells was higher than in cancer cells (median=5.0% vs. 0.0%; p=0.001), whereas PD-L2-positivity was higher in cancer cells than in immune cells (median=30% vs. 5.0%; p&amp;lt; 0.001). PD-L1 positivity in cancer cells and immune cells were positively correlated in TNBC (rho=0.69, p=0.04) but not in ER+ BC. Conversely, PD-L2 positivity in cancer cells and immune cells were positively correlated in ER+ BC (rho=0.68, p=0.001) but not in TNBC. TNBC diverged from ER+ BC by displaying higher PD-L1 positivity in immune cells (median=20.0% vs. 1.0%; p=0.004). By the conventional cut point for positivity of ≥1% for PD-L1 and PD-L2 in cancer cells or immune cells, all TNBC tumors were PD-L1-positive (9/9), with 8 also being PD-L2-positive. Of the 22 ER+ cases, 16 were PD-L2-positive, of which only 9 were also PD-L1-positive. Table 1. shows cross tabulation data for PD-L1 and PD-L2 status by BC subtype. Conclusions: PD-L1 and PD-L2 proteins show divergent expression and are not correlated in BC. Discordant PD-L2 and PD-L1 expression may be more common in ER+ BC than in TNBC. This finding justifies efforts to explore PD-L2 as a complementary marker to PD-L1 for improved prediction of response to PD-1 inhibitors, which may benefit patients with aggressive ER+ BC that are eligible for chemotherapy. Table 1. PD-L1 vs. PD-L2 Status by Breast Cancer Subtype Citation Format: Lubna Chaudhary, Julie Jorns, Yunguang Sun, Sailaja Kamaraju, Yee Chung Cheng, Amanda Kong, Tina Yen, Caitlin Patten, Chandler Cortina, Inna Chervoneva, Christopher Chitambar, Hallgeir Rui. PD-L1 and PD-L2 Protein Expression is Frequently Discordant in Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-13-05.

554 Background: Previous chart review studies have reported that adjuvant chemotherapy after NAC did not clearly increase OS in MIBC cases characterized by a lack of TD. There is an unmet need to develop biomarkers to guide adjuvant therapy for this patient population. High levels of expression of cell proliferation marker Ki-67 are associated with poor outcome in chemotherapy naïve bladder cancer. Expression of PD-L1 has been studied as a potential predictive biomarker for anti-PD1 or PD-L1 therapies in metastatic MIBC. We therefore studied Ki-67 and PD-L1 expression in post NAC radical cystectomy samples at Moffitt Cancer Center and correlate them with TD and OS. Methods: Tissue microarrays (TMAs) were constructed from 116 post NAC cystectomy samples. The expressions of Ki-67 were evaluated with immunohistochemistry (IHC) and considered positive if any of the cores per sample were stained positive for Ki-67. The Dako 22C3 assay was used for PD-L1 IHC and the combined positive score of 10 or above was considered positive for PD-L1. Results: The median survival of this cohort of 116 patients was 33.4 months (range: 1.13 -127 months). 40 patients (35%) had TD and 21 patients (18%) achieved pathological complete response. Using Cox regression for OS, positive Ki-67 expression in post NAC radical cystectomy sample was associated with poorer OS (hazard ratio=2.412, 95% CI:1.076-5.408, p=0.033), independent of the pathological N stage. Patients with Ki67/PD-L1 double-negative tumors had a significantly longer median OS of 98.2 months versus 29.9 and 26.9 months in PD-L1-/Ki67+ and PD-L1+/Ki67+ tumors respectively (Log-rank test, p=0.0361). Lack of TD was significantly associated with positive Ki-67 (P&lt;0.001) and positive PD-L1 (p=0.003) in the post NAC samples with a multi-variable logistic regression model. Conclusions: Positive Ki-67 and PD-L1 expressions in post NAC radical cystectomy samples were associated with inferior OS and absence of TD. Adjuvant anti-PD1 therapy either alone or in combination with chemotherapy would be indicated for this subset of patients.

PD-L1 expression and T cells infiltration in patients with uncommon EGFR-mutant non-small cell lung cancer and the response to immunotherapy

Objective To investigate the expressions of PD-1 and PD-L1 in colon cancer tissue and their relationship with clinicopathological features and prognosis, and to provide some references for the treatment of colon cancer. Methods The expressions of PD-1 and PD-L1 proteins and mRNA in resected colon cancer tissues and adjacent normal tissues collected from our hospital between June, 2011 and June, 2013 were detected by immunohistochemistry and real-time fluorescence quantitative PCR. The relationship between the expressions of PD-1 and PD-L1 proteins on one hand and clinicopathological characteristics on the other hand was analyzed. The relationship between the expressions of PD-1 and PD-L1 proteins on one hand and the prognosis of colon cancer on the other hand was analyzed. Results The positive expression rates of PD-1 and PD-L1 proteins in the colon cancer tissues were significantly higher than those in the adjacent tissues (both P 3cm, TNM stage Ⅲ-Ⅳ, and Ducks stage C-D were significantly higher than those in the tumors with diameter < 3 cm, TNM stage I-Ⅱ, and Ducks stage A-B (all P<0.05). The 5-year survival rates of the patients with positive and negative PD-1 expressions were 62.50% and 79.49%, respectively; the 5-year survival rate of the patients with positive PD-1 expressions was significantly lower than that of the patients with negative PD-1 expression (P<0.05). The 5-year survival rates of the patients with positive and negative PD-L1 expressions were 61.36% and 82.86%, respectively; the 5-year survival rate of the patients with positive PD-L1 were significantly lower than that of the patients with negative PD-L1 expression (P<0.05). Conclusion PD-1/PD-L1 pathway is an important mechanism of immunosuppression in colon cancer. Drug blockade of this pathway is beneficial to enhance the patients’ immune function, improve the therapeutic effect and prognosis. Key words: Colon cancer; Costimulatory molecules; PD-1; PD-L1

1252P - PD-L1 expression in uncommon EGFR-mutant non-small cell lung cancer and its response to immunotherapy

PD-1, PD-L1 and CTLA-4 in pregnancy-related – and in early-onset breast cancer: A comparative study

Introduction: Squamous cell carcinoma (SCC) is the most common skin cancer with a high rate of death. Different lymphocyte populations play an important role in modulating the immune response in the tumor microenvironment. The increase in the proportion of cluster of differentiation (CD)4+ CD25+ regulatory T-cell (Treg) lymphocytes is associated, in different studies, with the increase of the cell multiplication rate. Aim: To analyze the Treg lymphocyte subpopulations and to correlate the results with the presence of the CD8+ cytotoxic T-cell (Tc) lymphocyte population. Materials and Methods: Sixty primary skin SCC specimens were incubated with anti-CD8 (clone SP57) rabbit monoclonal antibody and anti-CD25 (clone 4C9) mouse monoclonal antibody. Results: The ratio of the intratumoral/peritumoral CD4+ CD25+ forkhead box protein p3 (Foxp3) lymphocytes was 0.46, emphasizing that at tumor margins, where tumor aggressiveness is higher, these lymphocytes subpopulations facilitate tumor progression. The comparative analysis of the tumor microenvironment profile revealed that in the case of intratumoral immune response, the number of Tc-type lymphocytes (CD8+) was 3.34 times higher compared to Treg lymphocytes (p<0001). In the peritumoral area, the number of Tc lymphocytes was 5.05 times higher compared to Treg lymphocytes (p<0001). Conclusions: Treg lymphocytes inhibition may cause the suppression of the antitumoral cell immune response in the tumor environment. We believe that Treg lymphocytes should represent a focus of interest for a new personalized therapy. New studies are needed to better understand the immune response in the tumor microenvironment.