A 55-year-old man presents with a 6-month history of progressive dysphagia, initially to solids and now to liquids. He reports unintentional weight loss of 5kg. He is an ex-smoker and drinks 20 units of alcohol per week. An upper GI endoscopy reveals a malignant-looking ulcerative lesion in the mid-oesophagus. Biopsies are taken. Which histological type of oesophageal cancer is most likely in this patient given the location and risk factors?