Lurbinectedin (PM01183) Combined With Pembrolizumab in Small Cell Lung Cancer.

Inclusion criteria 1. Male/female participants who are at least 18 years of age on the day of signing informed consent with histologically confirmed diagnosis of SCLC whose disease has progressed after first-line chemotherapy-based regimen will be enrolled in this study. 2. At least 4 weeks since the last anticancer therapy. 3. Male participants: a male participant must agree to use a contraception as detailed in Appendix 3 of this protocol during the treatment period and for at least 190 days after the last dose of study treatment and refrain from donating sperm during this period. 4. Female participants: a female participant is eligible to participate if she is not pregnant (see Appendix 3), not breastfeeding, and at least one of the following conditions applies: 1. Not a woman of childbearing potential (WOCBP) as defined in Appendix 3 OR 2. A WOCBP who agrees to follow the contraceptive guidance in Appendix 3 during the treatment period and for at least 7 months after the last dose of study treatment. 5. The participant (or legally acceptable representative if applicable) provides written informed consent for the trial. 6. Have provided archival tumor tissue sample or newly obtained core or excisional biopsy of a tumor lesion not previously irradiated. Formalin-fixed, paraffin embedded (FFPE) tissue blocks are preferred to slides. Newly obtained biopsies are preferred to archived tissue. Note: If submitting unstained cut slides, newly cut slides should be submitted to the testing laboratory within 14 days from the date slides are cut. 7. Have an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 to 1. Evaluation of ECOG PS is to be performed within 7 days prior to the date of allocation. 8. Have adequate organ function as defined in the following table (Table 1). Specimens must be collected within 10 days prior to the start of study treatment. 9. Recovery to NCI-CTCAE grade ≤1 or to baseline from any AE derived from previous treatment (excluding alopecia and/or cutaneous toxicity and/or peripheral sensory neuropathy and/or asthenia, all grade ≤2 and/or correctable electrolyte abnormality with supplementation). 10. Patients included in the expansion cohort at the RD (stage I) and all patients included in the stage II must have: 1. Measurable disease according to RECIST 1.1; and 2. Documented disease progression during or immediately after last therapy according to any of the aforementioned criteria. Exclusion criteria 1. A WOCBP who has a positive urine pregnancy test within 72 hours prior to allocation (see Appendix 3). If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required. 2. Has had prior treatment with or exposure to: a) PM01183. b) T-cell or other cell-based or biologic therapies. c) Experimental anti-tumor vaccines; therapies that target any T-cell co- stimulation or checkpoint pathways, such as anti-PD-1, anti-PD-L1, anti-PD- L2, anti-CD137, or anti CTLA-4 antibody, including ipilimumab; or other medicines specifically targeting T-cells. 3. Has received prior systemic anti-cancer therapy including investigational agents within 4 weeks prior to allocation. Note: Participants must have recovered from all AEs due to previous therapies to ≤Grade 1 or baseline. Participants with ≤Grade 2 neuropathy may be eligible. Note: If participant received major surgery, they must have recovered adequately from the toxicity and/or complications from the intervention prior to starting study treatment. 4. Has received prior radiotherapy within 2 weeks of start of study treatment. Participants must have recovered from all radiation-related toxicities, not require corticosteroids, and not have had radiation pneumonitis. A 1-week washout is permitted for palliative radiation (≤2 weeks of radiotherapy) to non-CNS disease. 5. Has had radiotherapy (RT) in more than 35% of the bone marrow. 6. Has a history of previous bone marrow and/or stem cell transplantation and allogenic transplant. 7. Has an impending need for RT (e.g., painful bone metastasis and/or risk of spinal cord compression). 8. Has received a live vaccine within 30 days prior to the first dose of study drug. Examples of live vaccines include, but are not limited to, the following: measles, mumps, rubella, varicella/zoster (chicken pox), yellow fever, rabies, Bacillus Calmette-Guérin (BCG), and typhoid vaccine. Seasonal influenza vaccines for injection are generally killed virus vaccines and are allowed; however, intranasal influenza vaccines (e.g., FluMist®) are live attenuated vaccines and are not allowed. 9. Has any of the following concomitant diseases/conditions: 1. History or presence of unstable angina, myocardial infarction, congestive heart failure, or clinically significant valvular heart disease within last year. 2. Symptomatic arrhythmia or any uncontrolled arrhythmia requiring ongoing treatment. 3. History of idiopathic, pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, idiopathic pneumonitis or evidence of active pneumonitis on screening chest CT-scan. History of radiation pneumonitis in radiation field (fibrosis) is permitted, as long as it is asymptomatic and no steroids are needed. 4. Known history of active neurologic paraneoplastic syndrome. 5. Myopathy or any clinical situation that causes significant and persistent elevation of CPK (\>2.5 x ULN in two different determinations performed one week apart). 6. Limitation of the patient's ability to comply with the treatment or follow-up protocol. 7. Any other major illness that, in the Investigator's judgment, will substantially increase the risk associated with the patient's participation in this study. 10. Is currently participating in or has participated in a study of an investigational agent or has used an investigational device within 4 weeks prior to the first dose of study treatment. Note: Participants who have entered the follow-up phase of an investigational study may participate as long as it has been 4 weeks after the last dose of the previous investigational agent. 11. Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drug. 12. Has a known additional malignancy that is progressing or has required active treatment within the past 5 years. Note: Participants with basal cell carcinoma of the skin, squamous cell carcinoma of the skin, carcinoma in situ (e.g., breast carcinoma, cervical cancer in situ) that have undergone potentially curative therapy are not excluded. 13. Has known active CNS metastases and/or carcinomatous meningitis. Participants with previously treated brain metastases may participate provided they are radiologically stable, i.e. without evidence of progression for at least 4 weeks by repeat imaging (note that the repeat imaging should be performed during study screening), clinically stable and without requirement of steroid treatment for at least 14 days prior to first dose of study treatment. Brain CT-scan or MRI results must be provided at baseline. 14. Has severe hypersensitivity (≥Grade 3) to pembrolizumab, PM01183 and/or any of their excipients. 15. Has active autoimmune disease that has required systemic treatment in the past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment. Exception: patients with vitiligo or resolved childhood asthma/atopy; patients who require intermittent use of bronchodilators or local steroid injections; and patients with hypothyroidism stable on hormone replacement or Sjögren's syndrome will not be excluded from the study. 16. Has a history of (non-infectious) pneumonitis that required steroids or has current pneumonitis. 17. Has an active infection requiring systemic therapy. 18. Has a known history of Human Immunodeficiency Virus (HIV). 19. Has a known history of Hepatitis B (defined as Hepatitis B surface antigen \[HBsAg\] reactive) or known active Hepatitis C virus (defined as HCV RNA is detected) infection. Note: no testing for Hepatitis B and Hepatitis C is required unless mandated by local health authority. 20. Has a known history of active tuberculosis (Mycobacterium tuberculosis). 21. Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the study, interfere with the subject's participation for the full duration of the study, or is not in the best interest of the subject to participate, in the opinion of the treating Investigator. 22. Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. 23. Is pregnant or breastfeeding or expecting to conceive or father children within the projected duration of the study, starting with the screening visit through 7 months after the last dose of trial treatment.