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Background: Patients with sensitive EGFR mutations are already being treated with first and second generation tyrosine kinase inhibitors (TKIs). However, resistance to these drugs occurs over time, and over half of all cases is caused by a mutation (T790M) in the EGFR kinase domain. Osimertinib offers a new treatment option that overcomes this problem. Unfortunately, resistance to this drug also develops after several months of treatment and is caused by another mutation (C797S) in EGFR., Case Report: Our case report provides evidence for the progressive development of EGFR-TKI resistance in a patient with a deletion of exon 19 in the EGFR gene. First, based on a mutation (T790M) identified after afatinib treatment and a subsequent mutation (C797S) mutation identified after osimertinib treatment. We mention overcoming this resistance (C797S) mutation by using 4th generation EGFR-TKI and other alternative procedures (chemotherapy, immunotherapy, and combinations of older EGFR-TKI generations). We also mention a rare case of peritoneal metastasis that occurred after previous treatment with osimertinib that we attempted to ameliorate by using erlotinib because the impaired condition of the patient did not allow treatment by chemotherapy. There are documented cases in which erlotinib has been successfully given to patients with peritoneal metastases and patients with the EGFR mutation C797S following progression to afatinib. This was not the case in our patient, probably because of the remaining EGFR mutation T790M., Conclusion: In our case report, erlotinib did not show efficacy after progression to osimetinib. Nowadays, chemotherapy is the only possible treatment in patients with good a performance status. The next-generation of TKIs are undergoing promising developments.Key words: EGFR - deletion on exon 19 - mutation T790M - mutation C797S - afatinib - osimertinibSubmitted: 12. 9. 2017Accepted: 12. 10. 2017 This project was supported by grant AZV 17-30 748A. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers.

Goblet cell carcinoid (GCC) of the appendix is extremely rare, representing approximately 5% of all primary appendiceal neoplasms. Histologically there are three groups of GCC: group A (typical GCC), adenocarcinoma ex GCC signet ring cell type (group B), and adenocarcinoma ex GCC poorly differentiated carcinoma type (group C), which is the most aggressive. GCC metastasizes in 15-60% of cases, mainly to the ovaries, pelvis, abdominal cavity, ribs, vertebrae, and lymph nodes. Hematogenous metastasis to the liver or other parenchymal organs can occur, but this is very rare. The different organs metastases havent been described yet. The primary mode of treatment is radical surgical resection or debulking, followed by chemotherapy; however, patients with unresectable or recurrent GCC are candidates for systemic therapy. Here, we report a case of very aggressive GCC of the appendix, which had metastazed to the liver at the time of diagnosis and subsequently metastasized to the orbit.