The evolving role of pemetrexed disodium for the treatment of non-small cell lung cancer

Giovanni Rossia, Angela Alamaa, Carlo Genova b, Erika Rijaveca, Marco Tagliamentoa, Federica Bielloa, Simona Cocoa, Maria Giovanna Dal Belloa, Simona Boccardoa and Francesco Grossib
aLung Cancer Unit, Ospedale Policlinico San Martino, Genoa, Italy; bMedical Oncology, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy

ABSTRACT

Introduction: Non-small cell lung cancer (NSCLC) remains one of the big cancer killers, despite the introduction of a number of approved therapeutics in recent times. Pemetrexed is a multi-target folate inhibitor, which is currently available to patients affected by advanced non-squamous NSCLC in combination with a platinum derivate in first-line therapy and as a single agent in second-line therapy.

Areas covered: This review covers presents the use pemetrexed in the management of NSCLC by exploring the data available from clinical trials and meta-analyses. Data from a phase III trial confirmed its role in the first-line setting in combination with immune checkpoint inhibitors (ICIs). Furthermore, data suggested a role for pemetrexed in local and advanced NSCLC.
Expert opinion: To date, in spite of the introduction of novel anti-neoplastic agents, pemetrexed still represents a cornerstone in the management of non-squamous NSCLC. Furthermore, recently published data support its role in innovative combinations including together with chemotherapy and immunotherapy.
ARTICLE HISTORY Received 28 May 2018 Accepted 12 October 2018
KEYWORDS Chemotherapy; immune- checkpoint inhibitors; non- small cell lung cancer; pemetrexed; platinum combination

 

 

1.Introduction
Non-small cell lung cancer (NSCLC) still represents the main cause of cancer-related death worldwide, with approxi- mately 154,000 estimated deaths in US in 2018 [1]. Platinum-based regimens have been the standard of treat- ment in all NSCLC stages since many years, and several compounds have been employed in combination with pla- tinum-derivates (cisplatin or carboplatin). Pemetrexed (Alimta®, MTA, LY231514) is a multi-targeted anti-folate agent, developed by Eli-Lilly and registered for the treat- ment of malignant pleural mesothelioma and non-squa- mous NSCLC [2]. Currently, pemetrexed is combined with cisplatin or carboplatin as first-line in advanced NSCLC and in locally advanced NSCLC. Furthermore, pemetrexed is used as a single agent for maintenance treatment after induction platinum-based chemotherapy and in second line. In this review we report the results of the main studies conducted in recent years with pemetrexed and we discuss the role of this agent in the decision-making algorithm in light of the results of immunotherapy and molecular target therapies. The literature from PubMed as well as from the ASCO, ESMO, AACR WCLC meetings and clinicaltrial.gov were reviewed through the keywords ‘pemetrexed,’ ‘lung neoplasms,’ ‘immune-checkpoint combination’ and ‘thymi- dylate synthase’. The most relevant meta-analyses were also discussed.

 
2.Pharmacology
2.1.Pharmacodynamics
Pemetrexed is a folate analog belonging to the antimeta- bolites class. The drug interferes with the synthesis of nucleic acids, resulting in a cytotoxic effect on neoplastic cells (Box 1). Pemetrexed competes with reduced folate, thereby significantly inhibiting the activity of multiple folate-requiring enzymes: thymidylate synthase (TS), dihy- drofolate reductase (DHFR), and glycinamideribonucleotide formyltransferase (GARFT) [3]. Additionally, another folate- dependent enzyme involved in purine synthesis, aminoimi- dazolecarboxamide ribonucleotide formyltransferase (AICART), has been reported to be a target for pemetrexed [4]. The primary pharmacologic target of pemetrexed is TS: an essential enzyme involved in DNA replication and cell growth. This enzyme converts deoxyuridylate (dUMP) to deoxythymidylate (dTMP), which is essential for the synth- esis of DNA [5]. The TS inhibition reduces dTMP and increases dUTP in cells, causing DNA strand breakage and apoptosis. Some data suggest that low expression of TS could predict responsiveness to pemetrexed in NSCLC patients [6–8]. Pre-clinical data show that pemetrexed is also able to induce the activation of caspase 2, 3, 8, and 9 in NSCLC cell lines, resulting in caspase-dependent apopto- sis through the activation of ataxia-telangiectasia mutated

 
CONTACT Angela Alama [email protected] Lung Cancer Unit, Ospedale Policlinico San Martino, Genoa, Italy
© 2018 Informa UK Limited, trading as Taylor & Francis Group
[2]. The elevation of transaminases and/or bilirubin has been

Box 1. Drug Summary. Drug name
Phase Indication
Pharmacology description Route of administration Chemical structure

Pemetrexed Launched
Non-Small Cell Lung Cancer Dihydrofolate reductase inhibitor Injectable/Intravenous
reported in 10–15% of treated patients; however, this eleva- tion is usually transitory and asymptomatic. Because peme- trexed is mostly eliminated through the kidneys, creatinine clearance (ClCr) should be evaluated (using the Cockroft and Gault formula): patients with ClCr ‡ 45 ml/min do not require dose adjustment; an insufficient number of patients with ClCr
<45 ml/min has received Pemetrexed in PARAMOUNT and JMDB trial; therefore, this drug should be avoided in this case. In addition, since nonsteroidal anti-inflammatory drugs

Pivotal trials [23,26,32]
Pharmaprojects – copyright to Citeline Drug Intelligence (an Informa busi- ness). Readers are referred to Informa-Pipeline (http://informa-pipeline.cite line.com) and Citeline (http://informa.citeline.com).
(ATM)/p53-dependent and (ATM)/p53-independent signaling pathways [3]. Several mechanisms of resistance to Pemetrexed have been reported: increased intracellular expression of TS, modification in the binding site of TS for the drug, decreased expression of the transporting proteins RFC and PCFT, and reduced polyglutamation of the drug [3,4].

2.2.Pharmacokinetics
Pemetrexed is administered by the intravenous route only; once infused, the drug is rapidly distributed within the body and peak plasmatic levels are reached within 30 min. Approximately 80% of the drug is bound to plasma proteins and its metabolites are rapidly eliminated (half-life: 3.5 h; total systemic clearance: 91.8 mL/min), mainly via the kidneys through glomerular filtration and active tubular secretion. Pemetrexed is mostly excreted through the urinary tract within 24 h from its administration, while a restricted amount of the drug is metabolized by the liver [9].

2.3.Toxicity
Pemetrexed is a well-tolerated drug. Its main adverse events are myelosuppression particularly neutropenia (18%-23% any grade), and thrombocytopenia (4–8% of any grade) [10]. It is well-known that vitamin supplement with folic acid (350–400 μg/day) and B12 (1000 μg every 9 weeks) from at least 1 week before the first cycle of treatment leads to a substantial reduc- tion of pemetrexed-related toxicity and do not reduce efficacy. Notably, an elevated pretreatment plasmatic level of homo- cysteine (a surrogate marker of functional folate deficiency) predicts severe, potentially life-threatening thrombocytopenia and neutropenia, associated or not with severe diarrhea and mucositis, while a high pre-treatment level of methylmalonic acid (a marker of vitamin B12 deficiency) is an independent predictor of severe diarrhea and mucositis both in patients receiving and not receiving vitamin supplement [11,12]. Pemetrexed is classified as an agent with low emetic-risk [13]. Skin rash has been observed, but it may be prevented through the prophylactic use of PO steroids; the equivalent dose of 4 mg BID of dexamethasone can be administered for three days, starting on the day before infusion of Pemetrexed
and aspirin may reduce the renal excretion of pemetrexed, potentially causing increased toxicity, their administration should be interrupted at least 2 days before pemetrexed and should not be restarted until at least 2 days after its adminis- tration [2,9]. Many cases of acute kidney injury have been reported in the literature; renal function could completely recover at the interruption of the treatment, but several cases of residual chronic renal damage were described [14].
3.Pemetrexed in advanced NSCLC
3.1.First line
Advanced NSCLC is currently considered incurable, and the treatment of choice is systemic therapy, usually consisting of platinum-based combinations for first-line treatment [15] or immunotherapy with pembrolizumab in patients with high expression of PD-L1. Pemetrexed was earlier studied as a single agent [16,17] and in combination with cisplatin [18,19]
and carboplatin [20] showing a favorable toxicity profile and activity in numerous non-randomized phase II trials. In parti- cular, the response rate (RR) was 24% when combined with cisplatin with a median survival of 13.5 months [20–22]. The pivotal trial was the JMDB: a randomized phase III trial com- paring one of the standard platinum-based regimens (cispla- tin-gemcitabine) with cisplatin-pemetrexed [23]. Taking into account the mild toxicity of Pemetrexed, the study was designed as a non-inferiority trial. Globally, 1725 eligible patients were randomized to receive cisplatin 75 mg/m2 and pemetrexed 500 mg/m2, both on day 1, every 3 weeks (with prophylactic use of folic acid and vitamin B12) or cisplatin 75 mg/m2 on day 1 and gemcitabine 1250 mg/m2 on days 1 and 8 every 3 weeks. A maximum of six cycles was allowed for both arms. Median overall survival (OS; the primary end-point) was non-inferior in the pemetrexed arm (10.3 vs 10.3 months; HR = 0.94; 95% CI 0.84–1.05). Considering patients with non- squamous histology (preplanned Cox proportional hazard model), median OS was 12.6 months in the cisplatin-peme- trexed arm and 10.9 months in the cisplatin-gemcitabine arm (HR = 0.84; 95% CI 0.71–0.99; p = 0.03). Based on these data, the combination of cisplatin and pemetrexed was registered in first line for the treatment of advanced non-squamous NSCLC (Table 1).
3.2.Maintenance
Pemetrexed maintenance until disease progression is currently the standard of care in the treatment of advanced NSCLC not progressed after induction chemotherapy. Switch and
Table 1. Relevant published randomized clinical trials of Pemetrexed in advance NSCLC.
Author Ph Regimens Pts Results
Scagliotti GV [23] III CisPem vs CisGem 1725 PFS: 4.8 m (CisPem) vs. 5.1 m (CisGem); HR = 1.04
OS: 10.3 m (CisPem) vs. 10.3 m (CisGem); HR = 0.94 Non-squamous (including adenocarcinoma and
large cell carcinoma):
PFS: 5.3 m (CisPem) vs. 4.7 m (CisGem); HR = 0.90
OS: 11.8 m (CisPem) vs. 10.4 m (CisGem); HR = 0.81; p = 0.005

Grønberg BH [22] III CarboPem vs
CarboGem
436 HrQoL similar between the two arms
OS: 7.3 m (CarboPem) vs. 7.0 m (CarboGem)

Zukin M [50] III CarboPem vs Pem
205 PFS: 5.8 m (CarboPem) vs. 2.8 m (Pem); HR = 0.46; p < 0.001 OS: 9.3 m (CarboPem) vs. 5.3 m (Pem); HR = 0.62; p = 0.001

Ciuleanu T [24] III Maintenance
Pem vs BSC
663 PFS: 4.3 (Pem) m vs. 2.6 m (BSC) vs 2.6 m; HR = 0.50; p < 0.0001 OS: 13.4 m vs. 10.6 m; HR = 0.79; p = 0.012

Paz-Ares L [25] III Maintenance
Pem vs BSC
539 PFS: 4.1 m (Pem) vs. 2.8 m (BSC); HR = 0.62; p < 0.0001

Barlesi F [27]
III
Maintenance
PemBev vs Bev
376
PFS: 7.4 m (PemBev) vs. 3.7 m (Bev); HR = 0.57; p < 0.0001 OS: 17.1 m (PemBev) vs. 13.2 m (Bev); HR = 0.87

Hanna N [38] III 2nd line Pem vs Docetaxel 571 PFS: 2.9 m (PEM) vs. 2.9 m (Docetaxel) HR = 0.97;
OS: 8.3 m (PEM) vs. 7.9 m (Docetaxel); HR = 0.99; non inferiority

Gandhi L [32] III Carbo/CisPem+ Pembrolizumab
vs
Carbo/CisPem+ Placebo
616 PFS: 8.8 m (Pembrolizumab) vs. 4.9 m (Placebo) HR = 0.52; p < 0.001 OS: NR(Pembrolizumab) vs. 11.3 m (Placebo) HR = 0.49; p < 0.001

Ph: phase of trial; Pts: number of patients; Cis: cisplatin; Carbo: carboplatin; Pem: pemetrexed; Gem: gemcitabine; Bev: bevacizumab; PFS: progression-free survival; OS: overall survival; m: months; HR: hazard ratio; HrQol: health-related quality of life; BSC: best supportive care; NR: not reached

 
continuation maintenance are the two available strategies in the clinical practice. In the switch modality, after first-line treat- ment, patients receive a different, non-cross-resistant agent. In a randomized, phase III trial of switch maintenance, 663 patients with stage IIIB/IV non-squamous NSCLC received pemetrexed or placebo after four cycles of chemotherapy [24]. First-line regimens included cisplatin doublets with gem- citabine, docetaxel or paclitaxel. Patients receiving pemetrexed achieved a significantly longer PFS (4.3 vs. 2.6 months; HR = 0.50; p < 0.0001) and OS (13.4 vs. 10.6 months; HR = 0.79; p = 0.012). The role of pemetrexed as continuation maintenance after first-line treatment was investigated in a randomized, double-blind, phase III trial (PARAMOUNT). Globally, 939 patients received four cycles of induction cispla- tin-pemetrexed followed by maintenance pemetrexed or pla- cebo if not progressed [25]. Median PFS from randomization (primary end point) was 4.1 months in the pemetrexed arm and 2.8 months in the placebo arm (HR = 0.62). Discontinuation due to unacceptable toxicity occurred in 5% of the patients receiv- ing pemetrexed. The final OS analysis resulted in a statistically significant benefit using pemetrexed compared to placebo (13.9 vs. 11.1 months; HR = 0.78) [26]. A recent meta-analysis on the safety of cisplatin-pemetrexed and maintenance of pemetrexed that include patients enrolled in the PARAMOUNT trial and JMDB identify on four cycles of induction followed by maintenance the better risk-benefit. Indeed, fati- gue, anemia, and renal events of grade 1–2 were increased for patients who received five or six cycles of combination com- pared to those patients receiving fewer cycles. Furthermore, treatment-related adverse events (AEs) were significantly more frequent in induction phase than in maintenance phase, and patients who developed AEs during induction phase did not experience worsening of symptoms during maintenance [4]. Other maintenance strategies were evaluated. In an open- label, randomized phase III trial (AVAPERL), 376 patients treated with a cisplatin-pemetrexed-bevacizumab combination in first-
line received maintenance with pemetrexed and bevacizumab or with bevacizumab alone [27]. PFS calculated after induction chemotherapy (primary end-point) was superior in the combi- nation arm (7.4 vs. 3.7 months; HR = 0.57; 95% CI 0.44–0.75 p < 0.0001) compared with bevacizumab alone. Median OS was 17.1 and 13.2 months (HR 0.87; CI 95% 0.63–1.21 p = 0.29), for the combination arm and for single-agent bevacizumab, respectively. However, pemetrexed monotherapy as mainte- nance was not included in this trial, thus the role of each single agent (pemetrexed and bevacizumab) and the potential advan- tage of the combination over pemetrexed alone could not be assessed [28]. After the promising results of a phase II trial with carboplatin, pemetrexed and bevacizumab, a phase III trial (POINTBREAK) with this regimen followed by maintenance with pemetrexed and bevacizumab compared with carboplatin, paclitaxel and bevacizumab followed by maintenance with bevacizumab were conducted [29]. The combination with pemetrexed showed a slightly improved PFS (6.0 vs. 5.6 months; HR = 0.83; p = 0.012), without difference in OS (12.6 vs. 13.4 months; HR = 1.0; p = 0.949). More recently, the PRONOUNCE phase III trial comparing the efficacy and safety of pemetrexed+ carboplatin followed by pemetrexed (Pem + Cb) with paclitaxel+ carboplatin+ bevacizumab followed by bevacizumab (Pac+ Cb+ Bev) in patients with advanced non- squamous NSCLC reported that Pem+ Cb was not significantly better in terms of PFS, OS, ORR, or DCR compared with Pac+ Cb + Bev. Both regimens were well tolerated but differed for toxicity profiles [30].
3.3.Pemetrexed in combination with immunotherapy
Recently, the activity of pembrolizumab (an anti-PD-1) in addi- tion to carboplatin and pemetrexed doublet was explored in a randomized phase II trial, Keynote 021 [31]. In this trial 123 advanced non-squamous NSCLC patients were randomly assigned to receive the doublet with or without pembrolizumab
200 mg flat dose. The ORR was 55% in the pembrolizumab arm versus 29% (p = 0.0016) in the standard arm. The median PFS was 13 versus 8.9 months (p = 0.01). Based on these results, a large randomized phase III trial in patients with previously untreated metastatic non-squamous NSCLC, without EGFR or ALK aberration was recently conducted. The Keynote 189 trial compared cisplatin or carboplatin and pemetrexed in combina- tion with pembrolizumab or placebo: the HR for death was 0.49 (95% CI 0.38–0.64 p < 0.001) with an estimated rate of survival at 12 months of 69.2% in the pembrolizumab arm versus 49.4% in the placebo arm. A significant difference in OS was seen in patients with tumor proportion of PDL-1 score (TPS) <1%, TPS = 1–49% and TPS> 50% with a HR of 0.59, 0.55 and 0.42, respectively. A significant difference in PFS was demonstrated for the pembrolizumab arm (8.8 months) compared to the placebo arm (4.9 months). The HR for disease progression or death was 0.52 (95% CI 0.43–0.64; p < 0.001). A better OS in favor of pembrolizumab was observed in all subgroups, while in terms of PFS patients aged more than 65 years and patients with a TPS <1% had not a statistically significant advantage. It is important to note that crossover was allowed: 32.5% of the patients treated in the placebo arm received pembrolizumab as a second-line and 40.3% of the patients received any immu- notherapy at disease progression. In spite of this, the advantage due to the addition of pembrolizumab in terms of OS was significant. The addition of pembrolizumab to the standard platinum and pemetrexed did not translate into worse toxicity. The rate of adverse events of any grade was 99.8% of with 67.2% grade 3–5 adverse events. Around 20% of the most severe events led to treatment discontinuation. In the experi- mental arm 27.7% of the patients discontinued the treatment due to adverse events compared to 14.9% (10.9% grade 3–5) in the standard arm [32]. Notably, the most frequent AE that occurred in greater frequency for the combination with pem- brolizumab than in the placebo group was renal dysfunction in the trial (blood creatinine increased: 12.2% vs. 7.6%; nephritis: 1.7% vs. 0%).
3.4.Pemetrexed in combination with EGFR tyrosine kinase inhibitors (TKI)
Cheng and colleague have investigated the combination of pemetrexed and gefitinib versus gefitinib alone in previously untreated patients affected by advance NSCLC with activating EGFR mutation [33]. The trial showed a longer PFS of the combi- nation with respect to gefitinib alone (15.8 vs. 10.9 months, HR = 0.68 p = 0.029). The results were not considered practice

changing [34]. since the difference of 5 months could be obtained with the sequential approach [35], furthermore the combination arm reported more grade 3–4 adverse events (42% vs. 19% p = 0.001) with two grade 5.

3.5.Second line
Pemetrexed has been evaluated in several second-line trials. After the positive results obtained in a single-arm trials [36,37], a randomized phase III study with pemetrexed compared with docetaxel was reported [38]. The primary end point was non- inferiority in OS: pemetrexed met the endpoints both in term of OS (HR = 0.78; 95% CI 0.61–1.00; p = 0.047) and PFS, with a good toxicity profile [39], except for the OS in the squamous subgroup (6.2 vs. 7.4 months; adjusted HR = 1.563; p = 0.018) [40]. Different schedules of pemetrexed have been compared to determine whether higher doses could be more effective: the dose of 900 mg/m2 and 1000 mg/m2 demonstrated a comparable efficacy, but reported more frequent adverse events than the standard dose.

4.Early stage
Pemetrexed have been evaluated in several phase II trials (Table 2). Well tolerated regimens were reported in most of the trials with a higher rate of patients completing the treat- ment than in other adjuvant trials [41,42]. Notably, in a rando- mized phase II trial (TREAT), 132 patients with radically resected NSCLC were randomized to receive adjuvant che- motherapy with cisplatin-vinorelbine or with cisplatin-peme- trexed; the primary end-point was feasibility rate (no G4 neutropenia or thrombocytopenia, or G3–4 febrile neutrope- nia or non-hematological toxicity), while secondary end-points were rug delivery and efficacy. The feasibility rate of cisplatin- pemetrexed was 95.5%, while the feasibility rate of cisplatin- vinorelbine was 75.4% (p = 0.001). After a follow-up of three years, no differences in efficacy outcomes were found [43].

5.Pemetrexed in locally advanced NSCLC
Locally advanced NSCLC is usually managed through com- bined modalities, including combinations of chemotherapy, radiotherapy, and surgery. Potentially resectable, stage IIIA NSCLC can be treated with neoadjuvant chemotherapy fol- lowed by surgical resection. Recently, a phase II trial evaluated the efficacy of pemetrexed in combination with carboplatin in early-stage NSCLC (Table 2). Forty-six patients were treated
Table 2. Relevant published clinical trials of Pemetrexed in early and locally advanced NSCLC.
Authors Ph Regimens Pts Results
Schmid-Bindert G [42] II Adj CisPem vs. CarboPem 118 FR: 59.4% (CisPem) vs. 50.0% (CarboPem)
Kreuter M [43] II Adj CisPem vs. CisVin 132 FR: 95.5% (CisPem) vs. 75.4% (CisVin); p = 0.001
Choy H [45] II CT-RT CarboPem-RT vs. CisPem-RT 98 TTP: 8.8 m (CarboPem) vs. 13.1 m (CisPem); p = 0.057
OS: 18.7 m (CarboPem) vs. N/A (CisPem)
Senan S [46] III CT-RT CisPem vs. CisEto 598 PFS: 11.4 m (CisPem) vs. 9.8 m(CisEto) HR = 0.86; p = 0.130
OS: 26.8 m (CisPem) vs. 25 m(CisEto) HR = 0.98; p = 0.831 Antonia SJ [47] III CT-RT + Durvalumab vs. CT-RT Placebo 703 PFS: 16.8m (Durvalumab) vs. 5.6 m (Placebo) HR = 0.52; p < 0.001
Ph: phase of trial; Pts: number of patients; Cis: cisplatin; Carbo: carboplatin; Pem: Pemetrexed; Vin: Vinorelbine; Eto: etoposide; CT-RT chemoteraphy plus radiotherapy; TTP: time to progression; PFS: progression-free survival; OS: overall survival; m: months; HR: hazard ratio; BSC: best supportive care; FR: feasibility rate; N/A: not assessable
with four cycles of chemotherapy before surgery. Fifty-nine percent of the patients underwent surgery after neoadjuvant chemotherapy. The treatment was well tolerated, and only one patient discontinued chemotherapy due to toxicity. The response rate was 41%, and OS rate at three years was 45% [44]. Unresectable locally advanced NSCLC can be treated with concurrent chemo-radiation or sequential chemotherapy and radiotherapy [45]. In a randomized, phase III trial, 600 stage III inoperable, non-squamous NSCLC patients were randomized to receive cisplatin-pemetrexed with concurrent thoracic radiotherapy followed by consolidation pemetrexed or cispla- tin-etoposide and concurrent radiation followed by a consoli- dation with an agent chosen by the investigator [46]. The primary end point was OS. OS was similar in the two arms with an HR of 0.98 (CI 0.79–1.20; p = 0.831); the median OS was 26.8 for pemetrexed combination and 25.0 months for the control arm, PFS was non-significantly longer in the peme- trexed arm (HR = 0.86; 95% CI 0.71–1.04; p = 0.130; median, 11.4 vs. 9.8 months) . The incidence of grade 3-4 adverse events was significantly lower in the pemetrexed arm (64% vs. 76.8%; p = 0.001).
Recently, in a randomized phase III trial, 713 stage III inop- erable NSCLC patients were randomized to receive durvalu- mab (an anti-PDL-1 inhibitor) or placebo after definitive chemo-radiotherapy: Median PFS was 16.8 months with dur- valumab versus 5.6 months with placebo with a HR for disease progression or death of 0.52 (95% CI 0.42–0.65 two-sided p < 0.001). The 18 months PFS rate was 44.2% with durvalu- mab and 27.0% with placebo. The PFS benefit was observed irrespective of PDL-1 expression before chemo-radiotherapy. In this population 4.2% of patients (8% of non-squamous NSCLC patients) underwent chemotherapy with pemetrexed combined with carboplatin or cisplatin [47].

6.Pemetrexed in elderly or unfit patients
In elderly patients, first-line chemotherapy with a platinum- based combination is frequently not feasible due to tolerabil- ity concerns. For this reason single-agent gemcitabine or vinorelbine are a common choice. In a randomized phase II trial, elderly patients received pemetrexed as single agent for eight cycles or pemetrexed for two cycles alternated with gemcitabine for two cycles for a total of eight cycles. Both schedules showed low response rate (4.5% and 11.6%, respec- tively) with a favorable tolerability [35]. Results from elderly patients with PS 0–1 treated with cisplatin-pemetrexed as a first-line treatment with or without pemetrexed as a mainte- nance treatment were analyzed in two previously reported trials [24,25]. In both studies, adjusted HR favored pemetrexed without important differences in older and younger patients. Treatment-related toxicities were similar between age sub- groups [48]. Sixty-two elderly patients received carboplatin- pemetrexed in a non-randomized, phase II trial. This combina- tion was active (RR = 28.6%; stable disease rate = 42.9%) with an acceptable tolerability [49]. In a randomized, phase III trial, 205 eligible PS = 2 patients received single-agent pemetrexed or carboplatin-pemetrexed. The combination achieved a bet- ter RR (23.8% vs. 10.3%; p = 0.019), a longer median PFS (5.8 vs. 2.8 months; HR = 0.46; p < 0.001) and a longer median OS

(9.3 vs. 5.3 months; HR = 0.62; p = 0.001). Toxicity was accep- table in both arms, with an increased incidence of hematolo- gic adverse events in the combination arm [50].

7.Conclusions
Pemetrexed is an antimetabolite employed in non-squamous NSCLC that affects the synthesis of DNA and RNA. The phar- macologic activity of this drug is correlated with the expres- sion of TS, such as in adenocarcinoma histology. Currently, pemetrexed is registered in combination with cisplatin or carboplatin as a first-line treatment for metastatic non-squa- mous NSCLC patients and soon the doublet will be adminis- tered also with pembrolizumab as standard of care; pemetrexed is also registered as a single agent for second- line treatment, and it represents a valid alternative with a good safety profile for patients who have not received the drug in first line [51]. Currently, pemetrexed is registered as adjuvant treatment in resected lung cancer. Preliminary data showed effectiveness as neoadjuvant treatment in early NSCLC patients [44]. Its favorable safety profile makes peme- trexed a feasible option for elderly patients [49]. Few data are available in locally advanced NSCLC: pemetrexed is not regis- tered in this setting, though the schedule in combination with platinum was available in the PACIFIC trial, potentially opening up new perspective in this setting.

8.Expert opinion
After its introduction into clinical practice, pemetrexed has become a standard of treatment in advanced non-squamous NSCLC. Its favorable safety profile, reported in many studies, has been widely confirmed in the clinical practice. Moreover, the good tolerability makes it a manageable option for elder and unfit patients [15]. Although these data were evidenced in wild-type NSCLC population, pemetrexed was also studied in combination with TKI in patients with activating EGFR muta- tions. Data regarding the combination with EGFR-TKI were considered formally positive, but they have never been applied to the clinical practice because of limited advantage associated with additional toxicity [33]. A recent phase I trial evaluating the safety and antitumor activity of pemetrexed combined with carboplatin and afatinib in NSCLC patients after EGFR TKI failure, showed a good safety profile, but it did not elucidate a better benefit of the combination respect to the standard of care [52]. Future trials should be warranted to identify the most effective combination and the specific clinical setting . The most significant revolution for the lung cancer treatment in 2018 has been shown in the Keynote 189 trial. The results of this trial suggest that the combination of immunotherapy to standard chemotherapy of pemetrexed and a platinum-based drug could be a well-tolerated treat- ment with the greatest efficacy ever seen in terms of PFS and OS for non-squamous NSCLC patients compared with che- motherapy alone. Several ongoing trials are evaluating the efficacy of new combinations with pemetrexed and immune checkpoint inhibitors in different scenarios: i.e. in EGFR mutated or ALK rearranged NSCLC patients progressing after TKI treatments [53,54], in adjuvant and neoadjuvant resectable
NSCLC [55]. However, these combination-schedules are not suitable for every NSCLC patients. In patients considered unfit for platinum-based chemotherapy, pemetrexed as single agent, could be a well-tolerated companion to be combined with immune checkpoint inhibitors, not only in second line (still ongoing), but also in first line, in order to improve the outcome of the most fragile patients [56,57].
In the light of the newest data and despite the advent of immunotherapy, pemetrexed will continue to be a corner- stone in non-squamous NSCLC treatment.

Funding

This manuscript was not funded.
Declaration of interest
F Grossi is on the advisory board of and has received speaker’s grants from Eli Lilly and Company, AstraZeneca, Merck Shark and Dohme, Bristol-Myers Squibb and Pierre Fabre. E Rijavec has received a speaker’s grant from AstraZeneca. C Genova has furthermore received honoraria from AstraZeneca, Bristol-Myers Squibb, Merck Sharp and Dohme and Roche. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.
Reviewer disclosures
Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

ORCID
Carlo Genova http://orcid.org/0000-0003-3690-8582
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