Lung cancer is the first cause of death in men and women, representing 28% and 26% of
      registered deaths worldwide, respectively. Among patients with this disease, at least 80% has
      non-small cell lung cancer (NSCLC), and 60% of patients are diagnosed when they already have
      a locally advanced or metastatic disease. NSCLC therapy regimens depend on the stage of
      disease and may require surgery, chemotherapy, radiotherapy, or a combination of these.
      Survival rate at 5 years is low for patients with stage II and III of the disease, with
      variation from 30% to 5%, this means that an improvement in therapy are required.

      Advances in molecular biology of cancer have led to discovering several molecular targets and
      developing new target therapies. Epidermal growth factor receptor (EGFR) is involved in the
      development and progression of several types of cancer, including NSCLC. However, despite
      clinical success with different tyrosine kinase specific domain inhibitors (TKIs), most of
      the patients respond to these drugs initially, but eventually develop resistance to these
      drugs after and average period of time of 10 months. Thus, innovative treatment strategies
      are required urgently to overcome therapeutic resistance to EGFR-TKIs and to improve survival
      of patients with NSCLC.

      Recently, metformin has been associated with reduction in the global risk of incidence and
      mortality of different types of cancer, due to its anti-tumor properties. In specific types
      of cancer, retrospective studies have demonstrated a clinical benefit from the use of
      metformin combined with the treatment of cancer.

      Patients with NSCLC with positive EGFR mutations are highly sensible to specific anti-EGFR
      tyrosine kinase inhibitors, however, most of the patients who initially respond to these
      target therapies, will present progression of the disease posteriorly during the treatment,
      this is known as acquired resistance. Acquired resistance to target therapies was first
      studied in patients with chronic myeloid leukemia with BCR-ABL translocation treated with
      Imitanib, an inhibitor of aberrant kinase BCR-ABL. Thanks to research, mutations associated
      with resistance to treatment with TKIs in NSCLC with positive EGFR mutations were discovered.
      By several studies, additional mutations were found in the kinase domain and in KRAS in those
      patients with acquired resistance to Gefitinib or Erlotinib. By PCR it was found that 50% of
      patients with resistance to TKI develop a specific mutation in exon 20 (T790M). However, the
      mechanism by which the other 50% of patients develop resistance to anti-EGFR TKI is yet
      unknown. Some studies have found focal amplification of MET proto-oncogen in 22% of the
      patients with acquired resistance to Gefitinib. The proposed mechanism is that MET
      amplification promotes resistance by activation of HER3 depending PI3K pathway. Nonetheless,
      there are few studies with few patients about MET amplification as a resistance mechanism.

      On the other hand, there are patients who have this resistance mutation since the first
      presentation, or de novo. T790M mutation may be present before exposition to TKI and it's
      generally found with other activating mutations in EGFR (exon 19 deletion and punctual L858R
      mutation). A response rate of 8% has been reported in those patients treated with gefitinib
      or erlotinib whose T790M mutation was positive at the time of the diagnosis, with
      progression-free survival of 2 months and global survival median of 16 months.

      Despite the advances in treatment have increased response rate and progression-free survival
      with anti-EGFR TKI in patients with presence of activating mutations, most of them will
      develop resistance mutations (T790M) and disease progression. There is no standard treatment
      in patients who progress from a first generation anti-EGFR TKI, such as erlotinib and
      gefitinib. Some studies have used afatinib as second line therapy in patients who had
      progression, finding a benefit in the progression-free survival, disease control rate up
      until 58% and delay in the development of lung cancer associate symptoms, thus improving
      quality of life in patients treated with afatinib.

      Acquired resistance will develop in a mean time of 9 to 13 months and the 50% to 60% will be
      secondary to development of T790M resistance mutation.

      The molecular mechanisms that generate acquired resistance to anti-EGFR TKI are not
      completely clear. We know that around 50% of cases are caused by an acquired mutation in the
      EGFR T790M and a lower percentage by MET oncogene amplification, nevertheless, there are
      other proposed molecular mechanisms, such as the activation of mesenchymal-epithelial
      transition. The latter, refers to changes in the phenotype of epithelial cells to cells with
      mesenchymal cells phenotype, resulting in increase in motility, proliferation and metastasis
      of tumor cells. It's been proposed that epithelial-mesenchymal (EMT) is associated with
      sensitivity to chemotherapy and TKI. Finding an effective therapy for patients who develop
      T790M resistance mutation is required to overcome resistance to first generation anti-EGFR
      TKI. Afatinib, as a second generation irreversible anti-EGFR TKI, has demonstrated in some
      studies to have certain effect in patients with resistance, however, the benefit is marginal.
      Studies have shown that the union of the tyrosine kinase portion of afatinib in patients with
      resistance mutation, is 100 times less strong that the union in cells with anti-EGFR
      activating mutations. Pre-clinical studies have demonstrated that inhibition of IL-6 receptor
      activation and activation of JAK1/STAT3 pathway overcomes resistance and sensitize again
      those cells with EGFR resistance mutation.

      Metformin is a drug that has been used for several years to treat diabetes mellitus and
      metabolic syndrome, it's generally well tolerated. Several studies since 1910 have suggested
      that patients with diabetes are at increased risk to develop cancer. The American Diabetes
      Association and The American Cancer Society have come to a consensus that suggests a clear
      association for greater risk of cancer incidence in diabetic patients. The tumors that have
      been studied with more frequency are in: colon, endometrium, rectus and breast. On the other
      hand, several epidemiologic and cases and control studies have suggested that the use of
      metformin decreases risk to develop cancer up until 30% with a hazard ratio (HR) of 0.77
      (0.64-0.92) and risk of cancer-specific death with a HR of 0.67 (0.53-0.85). Such protective
      effect has been seen in all kinds of cancer, but has been more studied in breast,
      gastrointestinal and lung cancer.

      The effect of metformin as chemo-prevention is subject to debate, however, there's more
      information about its use as adjuvant in the treatment of lung cancer, in combination with
      chemotherapy or target molecular therapy. Pre-clinical studies in mice have demonstrated that
      use of metformin per os may decrease the necessary dosage of chemotherapy and may prolong
      tumor remission. Metformin, by inhibiting repairing and anti-apoptosis mechanisms, increases
      sensitivity to chemotherapy, especially to platinum. Studies that involve metformin,
      paclitaxel, carboplatin and doxorubicin, have demonstrated to have an effect in tumor
      regression and prevention of recurrences up until four times the effect of monotherapy in
      xenograft models in cellular lines of lung and prostate cancer. Retrospective studies have
      found a benefit in progression-free survival and global survival in diabetic patients with
      NSCLC, who also are treated with metformin.

      T790M mutation and MET amplification are the main resistance mechanisms to anti-EGFR TKI,
      other mechanisms such as epithelial-mesenchymal transition (EMT) by TGF-β are resistance
      mechanisms. TGF-β also induces activation of IL-6 and paracrine activation of the receptor
      (IL-6R) and at the same time the activation of pathway JAK1/STAT3 and cell immortalization.
      Pre-clinical studies with cellular lines of lung cancer with anti-EGFR acquired-resistance
      treatment show that metformin prevents transcription of factors that activate
      epithelial-mesenchymal transition, inhibiting TGF-β, thus, inhibiting IL-6/JAK1/STAT3
      pathway, overcoming anti-EGFR TKI resistance in patients with T790M resistance mutation, in
      vitro and in vivo. A recent study reports that use of metformin in combination with gefitinib
      may increase efficacy of the latter, showing anti-proliferative and pro-apoptotic effect in
      cellular lines of NSCLC. Other studies have shown, by Western-blot, a decrease in levels of
      phosphorylation and activation of growth pathways MAPK, AKT and mTOR with the use of
      metformin, found in pre-clinical studies. Currently, a phase I/II study is being carried out
      to determine effective dose, safety and posteriorly the activity of metformin in combination
      with erlotinib as second line therapy in patients with NSCLC without EGFR mutation.

      The main objective of this study is to assess the progression-free survival period in
      patients with advanced non-small cell lung cancer in treatment with TKIs and metformin versus
      TKI alone. The secondary objectives are the response rate, global survival, quality of life,
      safety, as well as determining the alteration of nutrition parameters associated to the
      combined use of TKIs and metformin.

      Besides the secondary objectives, we want to find new candidate markers in the tumor
      characteristics to predict anti-tumor activity, as well as the search for serum biomarkers;
      among which we will analyze EGFR mutations (exon 18-21 mutations), IL-6, IGF-1, as well as
      determination of LKB-1 molecule expression in tumor tissue. We will associate the prognostic
      and potential role as possible biomarkers.