What is the optimal treatment approach for plasmacytoid variant of urothelial carcinoma?

Plasmacytoid Variant of Urothelial Carcinoma: Treatment Approach

Treat plasmacytoid variant urothelial carcinoma (PUC) with radical cystectomy plus neoadjuvant cisplatin-based chemotherapy for non-metastatic disease, and enfortumab vedotin plus pembrolizumab for metastatic disease, recognizing this as an aggressive variant with worse prognosis than conventional urothelial carcinoma.

Key Recognition Points

PUC is a rare and highly aggressive histologic variant that requires identification because of its potential for more aggressive natural history 1. This variant has a strong predilection for:

• Intra-abdominal and peritoneal spread 2
• Advanced stage at presentation (higher rates of T3-T4 disease and positive nodes) 3, 4
• Positive surgical margins (21% vs 4.1% in pure UC) 4

Treatment Algorithm by Stage

Non-Metastatic Disease (T2-4N0-3M0)

Primary approach: Neoadjuvant chemotherapy followed by radical cystectomy

1. Neoadjuvant chemotherapy is preferred (Category 1 recommendation for muscle-invasive disease) 5:

   • Use cisplatin-based regimens: ddMVAC with growth factor support (3-4 cycles) OR gemcitabine/cisplatin (4 cycles)
   • Despite PUC being traditionally considered chemoresistant, pathological downstaging occurs in 80% of cases 2
   • However, relapses remain common even with complete pathological response

2. Radical cystectomy with bilateral pelvic lymphadenectomy 1:

   • Must include common, internal iliac, external iliac, and obturator nodes at minimum
   • RC improves cancer-specific mortality (median survival 48 vs 38 months without RC) 3
   • Expect high rates of surgical upstaging and positive margins

3. Adjuvant chemotherapy for patients who did not receive neoadjuvant therapy and have high-risk pathology (pT3-4 or N+) 5, 6

Metastatic Disease (TanyNanyM1)

First-line: Enfortumab vedotin plus pembrolizumab 7, 8

• This combination is now preferred over platinum-based chemotherapy irrespective of platinum eligibility 7
• Recent case series demonstrates sustained stable disease in PUC patients treated with this combination 8
• Two of three PUC patients showed stable disease at 8-10 months with manageable adverse effects 8

Alternative for platinum-eligible patients:

• Cisplatin-based combination chemotherapy (gemcitabine/cisplatin or ddMVAC) 9, 7
• Median survival with chemotherapy in metastatic PUC: 11-13 months 3, 2

Both chemotherapy AND radical cystectomy improve outcomes in metastatic PUC:

• Median survival with RC: 12 vs 7 months without RC (HR 0.27, p<0.001) 3
• Median survival with chemotherapy: 11 vs 4 months without chemotherapy (HR 0.32, p=0.002) 3
• Consider cytoreductive surgery in highly selected metastatic patients

Critical Management Principles

Why PUC Requires Different Consideration

PUC should be managed similarly to conventional UC but with recognition of worse prognosis 1. The key differences:

• Higher disease burden at presentation: More likely to have T3-4 disease, positive nodes, and require neoadjuvant chemotherapy (46% vs 22% in pure UC) 4
• Peritoneal recurrence pattern: 19 of 23 patients (83%) with recurrence develop peritoneal carcinomatosis 2
• Median overall survival: 17.7 months overall; 45.8 months for stage I-III vs 13.3 months for stage IV 2

Common Pitfalls to Avoid

1. Do NOT withhold neoadjuvant chemotherapy based on historical data suggesting chemoresistance—80% achieve pathological downstaging 2

2. Do NOT use carboplatin instead of cisplatin in the perioperative setting—no data support this substitution 5, 1

3. Do NOT delay cystectomy in non-metastatic disease—surgery remains critical for local control despite high recurrence rates

4. Do NOT overlook peritoneal surveillance—this is the most common site of recurrence, occurring even after complete pathological response 2

Emerging Evidence

HER2 targeting may have a role: Preliminary data suggest PUC may have high HER2 expression levels, with one case report showing complete response to dual HER2-targeting therapy followed by enfortumab vedotin 10. However, this requires further validation.

Molecular features: Most PUC harbor TP53 (58%), TERT (38%), and CDH1 (35%) mutations 11. mTOR pathway mutations (PIK3CA, PIK3R1) are associated with significantly shorter survival and may represent therapeutic targets 11.

Surveillance After Treatment

Follow the standard post-cystectomy surveillance protocol 1:

• Imaging of chest, abdomen, and pelvis every 3-12 months for 2 years (based on recurrence risk)
• Pay particular attention to peritoneal surfaces given the high rate of peritoneal carcinomatosis
• Urine cytology, creatinine, and electrolytes every 3-6 months for 2 years

The aggressive biology of PUC mandates closer surveillance in the first 2 years when most recurrences occur.