**Core Concept**
The question requires knowledge of surgical management principles for gastric cancer, specifically the role of partial gastrectomy and distal pancreatectomy in treating tumors involving the stomach and pancreas. The underlying principle is to remove the tumor with adequate margins while preserving as much normal anatomy as possible.

**Why the Correct Answer is Right**
The correct answer involves a two-stage procedure: partial gastrectomy to remove the tumor from the stomach and distal pancreatectomy to remove the affected portion of the pancreas. This approach is chosen because the tumor involves the posterior wall of the stomach and extends 6cm up to the tail of the pancreas, indicating a need for both gastric and pancreatic resection. The goal is to achieve clear margins while minimizing the risk of recurrence. The pancreas is a critical organ, and resection should be limited to the affected portion to preserve pancreatic function.

**Why Each Wrong Option is Incorrect**
**Option A:** Closure of the abdomen would be an inappropriate response to a diagnosed tumor, as it would leave the cancer untreated and potentially allow it to progress.

**Option B:** Antrectomy, ulcers, and vagotomy are procedures used to treat peptic ulcer disease, not gastric cancer. This option would be insufficient for managing a tumor with pancreatic involvement.

**Option D:** Partial gastrectomy and distal pancreatectomy with splenectomy would be an overly aggressive approach, as the spleen is not directly involved in the tumor. Splenectomy is not necessary and would increase the risk of postoperative complications.

**Clinical Pearl / High-Yield Fact**
When managing gastric cancer with pancreatic involvement, it's essential to carefully assess the tumor's extent and involvement of surrounding structures to determine the optimal surgical approach. A multidisciplinary team, including surgeons, medical oncologists, and radiologists, should be involved in planning the treatment to ensure the best possible outcomes.

**✓ Correct Answer: C. Paial gastrectomy + Distal pancreatectomy**