A 38-year-old woman undergoes surgery for a WHO Grade II diffuse astrocytoma in the left temporal lobe. Postoperative MRI shows gross total resection. Molecular testing reveals IDH1 mutation and 1p/19q co-deletion. What is the preferred first-line adjuvant chemotherapy regimen?

Explanation

## Adjuvant Chemotherapy for 1p/19q Co-deleted Low-Grade Glioma **Key Point:** PCV (Procarbazine, Cisplatin, Vincristine) is the gold-standard adjuvant chemotherapy for WHO Grade II and III gliomas with 1p/19q co-deletion, particularly oligodendrogliomas. **High-Yield:** The RTOG 9402 and EORTC 26951 trials demonstrated that PCV chemotherapy followed by radiotherapy significantly improves progression-free survival and overall survival in patients with 1p/19q co-deleted gliomas compared to radiotherapy alone. This co-deletion is a strong predictor of chemosensitivity. ### Molecular Markers and Treatment Selection | Marker | Grade II/III Glioma | Preferred Adjuvant | Prognosis | |--------|-------------------|-------------------|----------| | **1p/19q co-deletion + IDH mut** | Oligodendroglioma | PCV + RT | Excellent (long PFS/OS) | | **IDH mutation alone (no 1p/19q)** | Astrocytoma | PCV or TMZ + RT | Intermediate | | **WT IDH + no 1p/19q** | Astrocytoma | PCV or TMZ + RT | Poor | | **Grade IV (GBM)** | Any | TMZ (Stupp protocol) | Poor | **Clinical Pearl:** 1p/19q co-deletion is almost pathognomonic for oligodendroglioma and indicates a chemosensitive tumor. IDH1/IDH2 mutations are favorable prognostic markers in lower-grade gliomas, conferring longer survival than IDH-wildtype tumors. ### PCV Regimen Details 1. **Procarbazine:** 75 mg/m² daily × 5 days 2. **Cisplatin:** 75 mg/m² on day 1 3. **Vincristine:** 1.4 mg/m² (max 2 mg) on day 1 4. **Cycle length:** 28 days, typically 6 cycles **Mnemonic:** **PCV = Procarbazine, Cisplatin, Vincristine** — the classic triplet for chemosensitive gliomas with 1p/19q co-deletion. ### Why PCV Over Temozolomide in This Context? - **1p/19q co-deletion predicts PCV sensitivity:** Oligodendrogliomas with this deletion respond exceptionally well to PCV, with long-term progression-free survival. - **Evidence base:** RTOG 9402 and EORTC 26951 specifically validated PCV for 1p/19q co-deleted tumors. - **Temozolomide:** While increasingly used as an alternative in some centers (especially for tolerability), it is not the standard of care for 1p/19q co-deleted gliomas; it is the standard for glioblastoma. **Warning:** Do not confuse the treatment algorithms: **PCV for 1p/19q co-deleted gliomas** vs. **Temozolomide for glioblastoma.** The molecular marker drives the choice. [cite:Robbins 10e Ch 28]