## **Core Concept**
The question describes a scenario where a patient has a persistent fear of having a serious illness, specifically gastric cancer, despite all radiological investigations indicating otherwise. This scenario points towards a psychiatric or psychological condition rather than an organic or physical illness.

## **Why the Correct Answer is Right**
The correct answer, **D.**, is likely related to a condition known as **Hypochondriasis** or **Illness Anxiety Disorder** as per DSM-5. This condition is characterized by excessive worry about having a serious illness despite medical reassurance and minimal or no somatic symptoms. The patient's preoccupation with the fear of having gastric cancer, despite negative investigations, fits well with this diagnosis. The condition involves a persistent fear of illness, which significantly impacts daily life.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Without the specific details of option A, it's difficult to provide a direct explanation. However, if option A refers to a different psychiatric condition that doesn't primarily involve fear of illness, it would be incorrect because it doesn't specifically match the scenario described.
- **Option B:** Similarly, without specifics, if option B refers to a condition more related to mood disorders or anxiety disorders not specifically focused on fear of illness, it would not be the best fit.
- **Option C:** If option C refers to a condition that is more related to somatic symptom disorder or another condition where the focus is on experiencing specific symptoms rather than fear of a specific disease, it would not accurately describe the scenario.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that patients with **Illness Anxiety Disorder** often require a therapeutic approach that includes cognitive-behavioral therapy (CBT) and sometimes selective serotonin reuptake inhibitors (SSRIs), in addition to repeated reassurance and education about their condition. It's also crucial to avoid excessive or unnecessary medical testing, which can reinforce their fears.

## **Correct Answer:** D. Illness Anxiety Disorder (or Hypochondriasis).