We present a case of extensive stage small cell lung cancer presenting as perforated appendicitis secondary to an appendiceal metastasis. This is a rare presentation with only six reported cases in the literature. Surgeons must be aware of unusual causes for perforated appendicitis as in our case the prognosis can be dire. A 60-year-old man presented with an acute abdomen and septic shock. Urgent laparotomy and a subtotal colectomy were performed. Further imaging suggested the malignancy was secondary to a primary lung cancer. Histopathology demonstrated a ruptured small cell neuroendocrine carcinoma in the appendix with thyroid transcription factor 1 positive immunohistochemistry. Unfortunately, the patient deteriorated due to respiratory compromise and was palliated day six postoperatively. Surgeons should consider a broad differential diagnosis for the cause of acute perforated appendicitis as this can rarely be due to a secondary metastatic deposit from a widespread malignant process.

Introduction and Importance: We present a case of extensive stage small cell lung cancer presenting as perforated appendicitis secondary to an appendiceal metastasis. This is a rare presentation with only 6 reported cases in the literature. Surgeons must be aware of unusual causes for perforated appendicitis as in our case the prognosis can be dire. Case Presentation: A 60-year-old man presented with an acute abdomen and septic shock. Computed tomography demonstrated perforated appendicitis and a widespread malignant process initially suspected as colonic origin malignancy. Urgent laparotomy and a subtotal colectomy was performed. Further imaging suggested the malignancy was secondary to a primary lung cancer. Histopathology demonstrated a ruptured small cell neuroendocrine carcinoma in the appendix with TTF1 positive immunohistochemistry. Unfortunately, the patient deteriorated due to respiratory compromise and was palliated on day 6 postoperatively. Discussion: The appendix is a rare site for metastasis of lung cancer and these metastases usually present as acute perforated appendicitis. Distinguishing the site of the primary tumor can be difficult when there is extensive metastatic disease, and this differentiation relies on immunohistochemistry. In our case the patient was managed surgically, however rapidly deteriorated post operatively from multi-organ metastatic disease. This demonstrates the diagnostic challenges in metastatic small cell lung carcinoma presenting as an acute appendicitis as well as the poor prognosis with advanced disease. Conclusion: Surgeons should consider a broad differential diagnosis for the cause of acute perforated appendicitis as this can rarely be due to a secondary metastatic deposit from a widespread malignant process.