Molecular Analysis for Targeted Therapy
In the present study, 629 tumor tissues were subjected to targeted treatment biomarkers’ analysis, using a 161 gene NGS panel. Successful molecular analysis was achieved in 610 of the 629 patients analyzed, while in 19 (3.03%) cases, no results could be obtained due to low DNA/RNA quality or quantity. The tumor types analyzed included common tumor types with targeted treatment available, such as lung, breast and colorectal cancer, but also various hard to treat diseases such as pancreatic, ovarian, prostate, brain cancers, sarcomas, cholangiocarcinomas, and others (Figure 1).
The mean age of test requisition was 60 years. In total, 936 pathogenic variants in 112 genes were detected in 472 patients (additional file 2). Of those, 85.15% were single nucleotide Variants (SNVs) or a small insertions-deletions (indels) detected at the DNA level, while 3.31% of the variants concerned gene fusions and 11.54% Copy Number Variations (CNVs). 11.54% of the 936 variants identified were classified as Tier 1, 86.75% of them as Tier 2 and 1.71% as Tier 3 (Figure 2). At least one variant was detected in 77.38% of the cases. 34.98% of the individuals analyzed carried one genomic alteration, while 23.81% and 19.87% carried two and three or more mutations respectively.
The main reason for multigene test request was the assignment of the appropriate treatment based on patients’ molecular profile. Thus, patients were apportioned based on the clinical significance of the alterations detected. In the case of multiple mutations present in the same patient, the variant with the higher level of evidence (LoE) was used for establishing the patient’s category. Using this biomarker-defined categorization, 54.59% of the patients analyzed received information that is related to on-label or off-label treatment (Tiers 1A.1, 1A.2, 1B, and 2C.1). Additionally, the variant detected could be used as a criterion for inclusion in clinical trials (2C.2) or is under investigation in preclinical studies (2D) in 21.48% and 1.80% of the cases respectively. Furthermore, 5.90% of the patients harbored a variant associated with resistance to treatment (1A.1R, 1A.2R) (Figure 3). As expected, the most frequently mutated gene in this cohort was the gatekeeper TP53 gene, followed by the KRAS and PIK3CA genes (Additional file 3). These genes were mutated in 36.39%, 24.75% and 10.98% of the patients, respectively (Figure 4). Furthermore, 7.38% of the patients carried an alteration in a gene involved in the homologous recombination pathway. This type of alterations could be used as predictive biomarkers of response to PARP inhibitors (PARPi) treatment (36,37).
Tissue specific tumor Molecular profile
In order to evaluate if molecular profile analysis is more useful in specific tumor types compared to others, the mutation frequency and clinical significance of the variants detected were calculated for the most common tumor types analyzed in our cohort.
I. Pancreatic Cancer
In the present study, 118 patients undertaking tumor molecular analysis had a diagnosis of pancreatic cancer. KRAS mutation was the prevalent mutated gene in this tumor type, with a mutation frequency of 74.57%. In 64.41% of the patients, an alteration in this gene was the finding with the higher LoE. However, other gene alterations with predictive value (2C.1) coexisted in 10.16% of the KRAS mutant patients. Moreover, in 6 cases (5.08%), the mutation detected was in an HR gene (1 ATM, 2 PALB2, 1 CDK12, 1 FANCA, 1 NBN) with evidence of response to PARPi. Additional variants with associated to off-label treatments were detected in FGFR1 & 4, HER2, MET, PIK3CA and POLE genes (Figure 5, additional file 4).
Furthermore, 2 patients (1.69%) carried a somatic mutation related to an on-label drug or with strong evidence of actionability. These mutations were detected in genes of the mismatch repair complex (MLH1 and MSH2) and were indicative of microsatellite instability and thus response to immunotherapy.
II. Lung Cancer
In the 67 Lung cancer, patients tested an alteration was detected in 86.57% of the cases (figure 5). The variant identified was related to an FDA approved treatment in 20.89% of the patients. These variants concerned EGFR, BRAF (p.V600) and HER2 mutations in percentages of 8.96%, 4.48% and 1.49%, respectively. Moreover, ALK and RET translocations were detected in 1.49% and 4.48% of the cases, respectively. EGFR TKI resistance-conferring KRAS mutations (Tier 1A.2) were detected in 26.87% of the cases. Apart from these established biomarkers, the expanded gene panel analysis was able to detect additional mutations in multiple other genes with 2C.1 evidence of predictive value in 16.42% of the cases (Additional file 5). Unexpectedly, 6 of the patients (8.95%) carried a mutation in a gene related to PARP inhibitor therapy.
III. Breast Cancer
In the 62 Breast Cancer Patients included in our cohort, a pathogenic variant was found in 80.65% of the cases. A Tier 1 variant was detected in 41.94% of the patients, while in 9.68% a Tier 2C.1 variant, related to off-label treatment, was identified. The most prevalent altered gene in these patients was the PIK3CA gene, with 33.87% mutation rate. Additionally, an HR gene alteration was present in 9.68% of the tumors analyzed (Additional file 6).
IV. Other Cancers
In the 44 patients with Colorectal cancer, the mutation rate was 84.09% (Figure 5, additional file 7). Eighteen patients (40.91%) carried a mutation in one of the RAS genes which are biomarkers of resistance to EGFR antibodies treatment (38,39). Additionally, three patients carried a targetable BRAF somatic mutation. One PMS2 positive tumor mutation was proven to be of germline origin, and thus it was considered eligible for immunotherapy treatment.
Among the 34 patients with prostate cancer, at least one somatic alteration was identified in 72.73% of them (Figure 5). In 5 cases, the mutation detected was in an HR gene (14.71%). Furthermore, 87.88% of the 33 patients with ovarian cancer, carried at least one somatic alteration. Four patients carried a mutation in BRCA1/2 genes, which are biomarkers of response to PARPi therapy, while in four patients, somatic mutations in off-label biomarkers were identified. Concerning brain tumors, the mutation rate was 77.78%. An alteration with associated potentially significant predictive biomarker was detected in 16 patients (62.96%) (Figure 5). However, in this tumor histology, the multigene analysis seems to confer not only predictive but also prognostic/diagnostic information (40,41). Genes with diagnostic significance are used by the World Health Organization Classification of Tumors of the Central Nervous System. For example, IDH1 and IDH2 mutations are used for distinguishing primary from secondary gliomas, while the simultaneous presence of IDH1/2 and TP53 alterations are distinctive of the diffuse astrocytoma histology (40).
Concerning the other histological types, even if the number of patients tested is small, it seems that in tumors of the endometrium (18 cases), esophagus (7 cases) and in cholangiocarcinoma (25 cases) the mutation rate is relatively high (94.44%, 71.43% and 72.00% respectively). On the contrary low mutation rates are observed in gastric tumors (30 cases), hepatocellular carcinomas (11 cases) as well as in the 30 sarcomas analyzed (64.71%, 54.55% and 50.00% respectively).
Panel comparison
The genetic information obtained by the 161 gene panel used in this study compared to that obtained from panels containing fewer genes was evaluated. At this regard, we conducted a simulation of the alterations that would have been detected if two smaller hotspot panels, of 24 and 50 genes respectively, had been used in the 610 patients analyzed (additional file 8).
If the 24 gene panel had been used in our cohort, a clinically significant variant (Tier 1 and 2) would have been detected in 58.85% of the cases. In comparison, this percentage would have been 62.62% by using the 50 gene panel. However, these rates are much lower than the 77.70% obtained by the 161 gene panel. Furthermore, considering the on-label and off-label biomarkers, the larger panel managed to detect 14.12% and 10.67% more on/off-label treatment-related biomarkers compared to the 24 and 50 gene panel respectively (Figure 6).
In order to evaluate if the number of genes analyzed is adequate for implementation in clinical practice, or if by increasing the number of genes tested a more informative result would have been obtained, we compared the actionability of our panel with a more comprehensive panel containing 501 DNA genes and 51 fusion drivers genes (38 of them also analyzed at the DNA level), for a total of 514 unique genes present in this panel (additional file 9).
Among the 990 patients with DNA sequencing results available, an SNV or indel alteration to a driver gene was obtained in 90.4% (895/990) of the cases using the whole genome sequencing approach of the study. In comparison the 161 gene panel would have detected such alterations in 72.12% of the patients and the larger panel 83.03%. At least one copy number variations would have been detected in 29.09% and 47.37% of the cases by the smaller (161 genes) and bigger panel (500+ genes) respectively. Both panels would have detected a fusion driver gene in 7.68% of the cases.
Considering all type of alterations (SNV, indel, CNV, gene fusion), at least one actionable alteration would have been identified in 80.00% of the samples if the 161 gene panel was used and in 90.10% of them if the 514 gene panel was implemented for the analysis (Figure 7). Furthermore, at least one clinically relevant biomarker, related to on/off-label treatment or to clinical trials would have been detected in 78.28% and 85.56% of the cases by the 161 and the 514 gene panels respectively.
Thus, the increase in the number of genes analyzed seems to increase the yield of patients who could benefit from targeted treatments.
Physicians Survey
Additionally, in order to investigate the implementation of tumor molecular profile analysis among physicians, a questionnaire was sent to referral oncologists asking whether they consider useful, such analysis for treatment decision making in various tumor types. 61 physicians responded to the survey. By far, the tumor type with the majority of positive responses was lung cancer, with 100% of the physicians responding that multigene panel should be performed for such tumor type (Table 2).
For colorectal cancer patients, a multigene analysis was considered useful in the primary or metastatic setting by 95.08% of the participants. For breast, ovarian, prostate and pancreatic cancers, the NGS utility was recognized by 80.33%, 80.32%, 90.16% and 95.08% of the participants respectively.
Immunotherapy biomarkers analysis
Tumor testing can give information for the selection of both appropriate targeted treatment and immunotherapy. The most known immunotherapies biomarkers are TMB, PD-L1 and MSI analysis. In the cohort of 610 patients with successful NGS testing for targeted therapy, 395 also requested TMB analysis. PD-L1 testing was performed in 198 cases, and MSI analysis in 201 patients. In 192 cases, all three immunologic biomarkers were analyzed (additional File 10) with successful analysis for all of them achieved in 191 cases.
Tumor Mutation Burden
Among the 395 patients with TMB analyzed, 14 cases (3.54%) could not receive a result due to the low quality of the genetic material analyzed. In these cases a high proportion (>60) of variants consistent with de-amination artifacts was detected, and thus these sequencing result could not be evaluated for TMB analysis, as indicated by the manufacturer (42). A successful TMB calculation was obtained for the remaining 381 patients.
The TMB value ≥10 muts/MB has been employed to separate high and low TMB values as indicated by the results of the open-label, phase 2 KEYNOTE-158 study that led to the recent FDA approval of Pembrolizumab for metastatic solid tumors (21). The median TMB value obtained was 5.60 (min 0; max 134), with 96 samples showing a TMB value higher than 10 muts/Mb and 285 samples with a lower than 10 muts/Mb value. The tumor type with the highest TMB median value in our cohort was colorectal cancer (median TMB=8.02), with 11 samples showing TMB>10 and 21 samples TMB<10 muts/Mb, followed by lung cancer (median TMB=7.72, 25 samples with TMB>10 and 22 with TMB<10 muts/Mb (Figure 8). The tumor types with the lowest TMB values were sarcomas, ovarian and pancreatic cancers (median TMB 3.43, 4.44 and 4.63 muts/Mb respectively). Accordingly, the positivity rates varied by tumor type with lung cancer showing the highest (42.55%) and soft tissue tumors displaying the lowest positivity rate (3.70%) (Figure 8).
PD-L1 expression
Among the 206 patients referred for PD-L1 analysis by immunohistochemistry, a successful analysis was achieved in 198 cases. PD-L1 positivity (>1%) was observed in 38.89% of them (77/988). Moreover, an intense PD-L1 expression was observed in 9.09% of the patients, exhibiting TPS values greater than 50% or CPS greater than 50.
In the 26 lung cancer patients tested 69.23% had a TPS value>1, with 19.23% showing an intense (>50%) PD-L1 expression. The positivity rate in various tumor types is illustrated in Figure 10. Among the 77 PD-L1 positive cases identified in our cohort 26 patients (33.77%) showed concomitant TMB positivity (>10muts/MB).
In accordance to previous studies, no association of TMB and PD-L1 values was observed (Figure 11) (43,44).
Microsatellite instability
Microsatellite instability was detected in 8 out of the 206 tumors tested (3.88%), while for one tumor the analysis failed due to the low quality of the genetic material obtained. Patients with tumors showing MSI high status had a diagnosis of Ovarian cancer, Pancreatic cancer, Colorectal cancer, Prostate cancer, Gastric cancer and Sarcoma. In 2 cases, the tumor instability was linked to hereditary mutations in MMR genes (MSH2 and PMS2). TMB analysis data were also available in 7 of these patients with 6 of them showing high TMB value (>13.46muts/MB). Thus a strong correlation between TMB and MSI was observed with MSI high tumors showing higher median TMB values, in accordance with previous studies (45,46). However, it should be noted that among the 193 MSI stable patients with TMB data available, high TMB values were also observed in 42 cases (Figure 11). This is of great importance, given the higher rate of positivity for this biomarker and the strong evidence of predictive value; thus, its use could identify more patients eligible for immunotherapy uptake.
Immunotherapy Biomarkers’ comparison
Among the 191 patients with all three immunotherapy biomarkers tested, ICIs option based on TMB result could be considered in 44 patients (23,04%), 26 of them with simultaneous PD-L1 positivity. Furthermore, 51 additional patients showed PD-L1 positivity and 1 MSI-high result. Collectively, positivity to one of these biomarkers and thus a possibility of benefit from ICIs treatment was observed in 50,26% (96/191) of these patients.
Furthermore, in these patients tested for biomarkers related to both targeted treatment and immunotherapy, an actionable finding (Tier 1 or 2) was detected in 83.25% of the cases. Moreover, the addition of the immunotherapy biomarkers to the molecular profile analysis increased the number of patients with an on-label treatment recommendation by 22.40% (Figure 12). TMB analysis increased the LoE of treatment recommendations to 1A.1 in 35 cases, with 22 of them showing concomitant PD-L1 positivity.