A 68-year-old woman presents to the emergency department with a several-month history of progressive fatigue, unintentional weight loss, and changes in bowel habits, now exacerbated by a week of severe, diffuse abdominal pain. She reports chronic constipation alternating with loose stools, and recently noticed dark, tarry stools mixed with brighter red blood. Her past medical history is significant for untreated hypertension and a 40-pack-year smoking history. She has avoided medical attention for years. On examination, she appears cachectic with scleral icterus and a yellowish discoloration of the skin. Vital signs include: blood pressure 185/110 mmHg, pulse 95/min, respirations 18/min, temperature 37.8°C, and oxygen saturation 97% on room air. Abdominal exam reveals diffuse tenderness, more prominent in the right upper quadrant, with rebound tenderness. A firm, irregular mass is palpable 5 cm below the right costal margin. Digital rectal exam reveals melanotic stool. Peripheral edema is noted. Given these findings, what is the most likely underlying diagnosis and the most appropriate immediate diagnostic study to confirm the primary source?

A 58-year-old male presents to a primary care office reporting intermittent bright red blood in his stools for the past two months. He describes seeing a small amount of blood on the toilet paper and sometimes coating the stool. He also mentions experiencing mild fatigue recently and a slight, unquantified change in bowel habits, noting stools are occasionally thinner than usual. His family history is significant for a paternal uncle diagnosed with colon cancer at age 62. The patient denies any weight loss, abdominal pain, or fever. He has a history of controlled hypertension and exercises regularly. On examination, his temperature is 36.80C, blood pressure is 128/78 mmHg, pulse is 76/min, respirations are 15/min, and oxygen saturation is 99% on room air. Digital rectal examination reveals external hemorrhoids with no palpable masses in the rectal vault. The stool obtained from the DRE is guaiac negative. His abdomen is soft, non-tender, and non-distended with normoactive bowel sounds. Given these findings, what is the most likely diagnosis and the most appropriate initial diagnostic approach?

A 68-year-old woman presents to her general practice clinic for a routine wellness visit. She reports feeling generally well but has noticed a gradual onset of increasing fatigue over the past six months, which she initially attributed to her busy schedule. She also mentions an unintentional weight loss of approximately 3 kg over the same period and occasionally describes vague, intermittent lower abdominal discomfort and a subtle change in bowel habits towards looser stools, although without frank melena or hematochezia. Her past medical history includes essential hypertension, managed with amlodipine, and a family history notable for a paternal aunt with colon cancer diagnosed in her early 70s. She denies smoking and consumes alcohol occasionally, about one glass of wine per week. On physical examination, her temperature is 37.0°C, blood pressure is 138/88 mmHg, pulse is 72/min, respirations are 16/min, and oxygen saturation is 98% on room air. She appears pale but is in no acute distress. Abdominal examination reveals no masses or tenderness. Digital rectal exam is negative for gross blood. Laboratory values are obtained to investigate her symptoms. Considering these findings, what is the most appropriate diagnostic approach and immediate management strategy?

A 68-year-old woman presents to her general practitioner reporting persistent sleep disturbances over the past four months. She describes an irresistible urge to move her legs, particularly in the evenings and during periods of rest, which is temporarily relieved by walking or stretching. Her partner observes her frequently shifting her legs during sleep, often causing awakenings for both of them. Over the same period, she notes a mild but continuous fatigue and an unexplained weight loss of 5 kg, despite no changes in her dietary habits or activity level. Her medical history includes well-controlled type 2 diabetes and osteoarthrosis. She denies any overt gastrointestinal bleeding but reports intermittent changes in bowel habits, alternating between constipation and softer stools, which she attributes to her diet. Her last screening colonoscopy was 18 years ago. On examination, her vital signs are stable: temperature 37.0°C, blood pressure 128/78 mmHg, pulse 76/min, and respirations 16/min. Physical examination reveals conjunctival pallor and mild nail bed changes. Abdominal examination is unremarkable with no masses or tenderness. Neurological examination is normal. Laboratory results are pending. Given these findings, what is the most appropriate next step in both diagnosing the underlying cause and initiating her subsequent management?