**Question:** Lymph node metastasis is least commonly seen with -

A. Breast cancer
B. Prostate cancer
C. Thyroid cancer
D. Ovarian cancer

**Core Concept:**
Lymph node involvement is a crucial aspect of cancer staging and prognosis. In oncology, cancer cells can spread via the lymphatic system to regional lymph nodes, potentially leading to lymph node involvement. Lymph node involvement can be assessed clinically and radiologically to help guide treatment decisions. The question is asking which type of cancer is least likely to involve lymph nodes.

**Why the Correct Answer is Right:**
Lymph node involvement in cancers is determined by various factors, including the primary tumor site, its size, and histopathological characteristics. Ovarian cancer typically involves the peritoneal cavity rather than lymph nodes, which makes it the least common type to cause lymph node involvement.

**Why Each Wrong Option is Incorrect:**
- Breast cancer can involve regional lymph nodes, but it is still more common than ovarian cancer.
- Prostate cancer often spreads to bone and distant organs, but it can also involve lymph nodes. The extent of lymph node involvement is more common than in ovarian cancer.
- Thyroid cancer is less likely to spread to lymph nodes compared to cancers of the breast, prostate, or thyroid. However, it is more common than ovarian cancer.

**Why the Correct Answer is Right:**
Ovarian cancer is less likely to spread to lymph nodes due to its unique pathophysiology. Unlike most other cancers, ovarian cancer primarily spreads through the peritoneal cavity, allowing cancer cells to disseminate directly into the peritoneal cavity. This characteristic makes ovarian cancer less likely to involve lymph nodes as compared to other cancers like breast, prostate, thyroid, or lung cancer.

**Correct Answer: D. Ovarian cancer**

**Why Each Wrong Option is Incorrect:**

- Breast cancer (A) is more likely to spread to lymph nodes, as it can directly invade and involve adjacent lymph nodes.
- Prostate cancer (B) can also spread to lymph nodes, and its incidence is higher than ovarian cancer but lower than breast cancer.
- Thyroid cancer (C) is less likely to spread to lymph nodes compared to breast, prostate, or lung cancer; however, it remains more likely than ovarian cancer.
- Lung cancer (D) is known to spread to lymph nodes more often than ovarian cancer.