Inclusion Criteria:
* Male or female, aged ≥ 18 years old and ≤ 75 years.
* ECOG Scale (Eastern Cooperative Oncology Group) of performance status of 0 or 1.
* Histologically or cytologically confirmed, non-resectable Stage IIIA-IIIB NSCLC according to the 8th version of the International Association for the Study of Lung Cancer Staging Manual in Thoracic Oncology.
* PET-CT (Positron Emission Tomography -Computed tomography) and brain computed tomography or Magnetic resonance imaging (MRI) at baseline to confirm the absence of distant disease.
* Mediastinal involvement could be considered without histological confirmation when no margin can be distinguished in the lymph node mass.
* No prior treatment with anti-neoplastic drugs or thoracic radiotherapy for Stage IIIA-IIIB NSCLC.
* Patients who have received prior neo-adjuvant, adjuvant chemotherapy with curative intent for non-metastatic disease must have experienced a treatment-free interval of at least 6 months from enrollment since the last chemotherapy.
* Presence of at least one measurable disease by CT-SCAN, as defined by RECIST v1.1.
* Adequate hematologic and organ function defined by the following laboratory results obtained within 14 days prior to enrollment:
* Neutrophils ≥ 1500 cells/μL without granulocyte colony-stimulating factor support.
* Lymphocyte count ≥ 500/μL.
* Platelet count ≥ 100,000/μL without transfusion.
* Haemoglobin ≥ 10.0 g/dL. Patients may be transfused to meet this criterion.
* INR or aPTT ≤ 1.5 × upper limit of normal (ULN). This applies only to patients who are not receiving therapeutic anticoagulation; patients receiving therapeutic anticoagulation should be on a stable dose.
* AST, ALT, and alkaline phosphatase ≤ 2.5 × ULN, with the following exceptions:
* Serum bilirubin ≤ 1.5 × ULN. Patients with known Gilbert disease who have serum bilirubin level ≤ 3 × ULN may be enrolled.
* Serum creatinine ≤ 1.5 × ULN or creatinine clearance of ≥60ml/min (based on the Cockcroft Gault formula).
* All patients are notified of the investigational nature of this study and signed a written informed consent in accordance with institutional and national guidelines, including the Declaration of Helsinki prior to any trial-related intervention.
* Adequate lung function: Forced Expiratory Volumen in 1 second (FEV1) \>50% of normal volume and Diffusion Capacity of the Lungs for Carbon Monoxide (DLCO) \>40% of normal value.
* No more than 35% of the total volume of the two lungs should receive more than 20 Gy (V20) or no more than 7cm maximum diameter.
* For female patients of childbearing potential, agreement (by patient and/or partner) to use a highly effective form(s) of contraception that results in a low failure rate (\< 1% per year) when used consistently and correctly, and to continue its use for 6 months after the last dose of trial treatment. Such methods include: combined (oestrogen and progesterone containing) hormonal contraception, progestogen-only hormonal contraception associated with inhibition of ovulation together with another additional barrier method always containing a spermicide, intrauterine device (IUD): intrauterine hormone-releasing system (IUS), bilateral tubal occlusion, vasectomised partner (on the understanding that this is the only one partner during the whole study duration), and sexual abstinence.
* For male patients with female partners of childbearing potential, agreement (by patient and/or partner) to use a highly effective form(s) of contraception that results in a low failure rate \[\< 1% per year\] when used consistently and correctly, and to continue its use for 6 months after the last dose of trial treatment. Male patients should not donate sperm during this study and for at least 6 months after the last dose of trial treatment.
* Oral contraception should always be combined with an additional contraceptive method because of a potential interaction with the study drugs. The same rules are valid for male patients involved in this clinical study if they have a partner of childbirth potential. Male patients must always use a condom.
* Women who are not postmenopausal (≥ 12 months of non-therapy-induced amenorrhea) or surgically sterile must have a negative serum pregnancy test result within 8 days prior to initiation of study drug.
Exclusion Criteria:
* Patients with known sensitizing mutation or an amplification in the epidermal growth factor receptor (EGFR) gene, ALK fusion oncogene.
* Known STK-11 ligand alterations, MDM2 amplifications or ROS1 translocations.
* Weight loss \>10% within the previous 3 months.
* Malignant pleural effusion or pericardial effusion: both will be considered as suggestive of metastatic disease. Also excluded those with negative cytology but being exudates.
* Patients with non-visible by thoracic X-Ray pleural effusion or too small to be safely punctioned could be included.
* Malignancies other than NSCLC within 3 years prior to enrollment, with the exception of those with a negligible risk of metastasis or death (e.g., expected 3-year OS \> 90%) treated with expected curative outcome (such as adequately treated carcinoma in situ of the cervix, basal or squamous-cell skin cancer, localized prostate cancer treated with radiotherapy or surgically with curative intent, ductal carcinoma in situ treated surgically with curative intent).
* Women who are pregnant, lactating, or intending to become pregnant during the study.
* Known hypersensitivity or allergy to biopharmaceuticals produced in Chinese hamster ovary cells or any component of the Atezolizumab formulation.
* History of autoimmune disease.
* History of idiopathic pulmonary fibrosis, organizing pneumonia (e.g., bronchiolitis obliterans), drug-induced pneumonitis, idiopathic pneumonitis, or evidence of active pneumonitis on screening chest CT scan.
* Positive test for human immunodeficiency viruses (HIV). All patients will be tested for HIV prior to inclusion into the study; patients who test positive for HIV will be excluded from the clinical study.
* Patients with active hepatitis B (chronic or acute; defined as having a positive hepatitis B surface antigen \[HBsAg\] test at screening) or hepatitis C.
* Patients with past hepatitis B virus (HBV) infection or resolved HBV infection (defined as the presence of hepatitis B core antibody \[HBcAb\] and absence of HBsAg) are eligible only if they are negative for HBV DNA (vaccinated patients are excluded).
* Patients positive for hepatitis C virus (HCV) antibody are eligible only if PCR is negative for HCV RNA.
* Active tuberculosis.
* Symptomatic neuropathy (sensory) grade \> 1 according to the NCI Common Toxicity Criteria for Adverse Events v5.0
* Severe infections within 4 weeks prior to be included in the study, including but not limited to hospitalization for complications of infection, bacteraemia, or severe pneumonia.
* Received therapeutic oral or IV antibiotics within 2 weeks prior to be included in the study.
* Patients receiving prophylactic antibiotics (e.g., for prevention of a urinary tract infection or to prevent chronic obstructive pulmonary disease exacerbation) are eligible.
* Significant cardiovascular disease, such as New York Heart Association cardiac disease (Class II or greater), myocardial infarction, or cerebrovascular accident within 3 months prior to inclusion, unstable arrhythmias, or unstable angina.
* Patients with known coronary artery disease, congestive heart failure not meeting the above criteria, or left ventricular ejection fraction \< 50% must be on a stable medical regimen that is optimized in the opinion of the treating physician, in consultation with a cardiologist if appropriate.
* Patients with a superior vena cava syndrome.
* Major surgical procedure other than for diagnosis within 28 days prior to inclusion or anticipation of need for a major surgical procedure during the course of the study.
* Prior allogeneic bone marrow transplantation or solid organ transplant.
* Administration of a live, attenuated vaccine within 4 weeks before inclusion or anticipation that such a live attenuated vaccine will be required during the study.
* Any other diseases, metabolic dysfunction, physical examination finding, or clinical laboratory finding giving reasonable suspicion of a disease or condition that contraindicates the use of an investigational drug or that may affect the interpretation of the results or renders the patient at high risk from treatment complications.
* Patients with illnesses or conditions that interfere with their capacity to understand follow and/or comply with study procedures.
* Treatment with any other investigational agent with therapeutic intent within 28 days prior to initiation of study treatment.
* Treatment with systemic immunosuppressive medications (including but not limited to corticosteroids, cyclophosphamide, azathioprine, methotrexate, thalidomide, and anti-tumor necrosis factor \[anti-TNF\] agents) within 2 weeks prior to inclusion.
