Okay, let's tackle this question about synovial sarcoma and its cellular markers. First, I need to recall what synovial sarcoma is. It's a type of soft tissue sarcoma, right? Commonly found near joints, but the name can be misleading because it's not always from synovial cells. The key here is the cellular markers.

The main marker for synovial sarcoma is the SS18-SSX fusion protein. This comes from a chromosomal translocation, specifically t(X;18)(p11;q11), which is pretty characteristic. So the correct answer should be the option that mentions SS18-SSX.

Now, the other options. Let's think about other markers. CD99 is positive in synovial sarcoma, but it's also seen in other tumors like Ewing's sarcoma. So CD99 alone isn't specific. Then there's Bcl-2, which is positive in some cases, but again, not specific. The S-100 protein is more associated with melanomas and schwannomas. So if an option lists S-100, that's probably incorrect.

The clinical pearl here is that the SS18-SSX fusion is a hallmark and can help in diagnosis. Also, the translocation is important for distinguishing it from other sarcomas. So the high-yield fact is the translocation and the fusion protein.

Wait, the user didn't provide the options, but the correct answer is mentioned as SS18-SSX. So in the explanation, I need to structure it with the correct answer section and explain why others are wrong. Make sure to mention the translocation and the fusion protein. Also, clarify that CD99 is present but not specific. S-100 is a common distractor in other sarcomas. Bcl-2 might be present but again not specific.

Need to check if there are other possible markers. For example, some sources mention that synovial sarcoma can express vimentin and keratins, but those are more general. The key is the SS18-SSX. So the core concept is the specific translocation leading to the fusion protein.

In the clinical pearl, emphasize that the presence of SS18-SSX in immunohistochemistry or FISH is diagnostic. That's a high-yield point for exams. Also, the translocation is a key differentiator from other sarcomas.

Make sure each section is concise, and the explanation is clear for a postgraduate student. Avoid jargon where possible but use precise terms. Check that the answer sections are correctly labeled and that each incorrect option is addressed with why it's wrong.

**Core Concept**
Synovial sarcoma is a soft tissue malignancy characterized by a specific chromosomal translocation, t(X;18)(p11;q11), leading to the **SS18-SSX fusion protein**. This fusion gene is a hallmark diagnostic marker and distinguishes synovial sarcoma from other sarcomas.

**Why the Correct Answer is Right**
The **SS18-SSX fusion protein** results from the t(X;18)(p11;q11) translocation, which is present in nearly all synovial sarcomas.

✓ Correct Answer: D. All