BackgroundTo assess the feasibility of elective neck irradiation to level Ib in nasopharyngeal carcinoma (NPC) using intensity-modulated radiation therapy (IMRT).MethodsWe retrospectively analyzed 1438 patients with newly-diagnosed, non-metastatic and biopsy-proven NPC treated with IMRT.ResultsGreatest dimension of level IIa LNs (DLN-IIa) ≥ 20 mm and/or level IIa LNs with extracapsular spread (ES), oropharynx involvement and positive bilateral cervical lymph nodes (CLNs) were independently significantly associated with metastasis to level Ib LN at diagnosis. No recurrence at level Ib was observed in the 904 patients without these characteristics (median follow-up, 38.7 months; range, 1.3–57.8 months), these patients were classified as low risk. Level Ib irradiation was not an independent risk factor for locoregional failure-free survival, distant failure-free survival, failure-free survival or overall survival in low risk patients. The frequency of grade ≥ 2 subjective xerostomia at 12 months after radiotherapy was not significantly different between low risk patients who received level Ib-sparing, unilateral level Ib-covering or bilateral level Ib-covering IMRT.ConclusionLevel Ib-sparing IMRT should be safe and feasible for patients without a DLN-IIa ≥ 20 mm and/or level IIa LNs with ES, positive bilateral CLNs or oropharynx involvement at diagnosis. Further investigations based on specific criteria for dose constraints for the submandibular glands are warranted to confirm the benefit of elective level Ib irradiation.

MRI-detected skull-base invasion is not an independent prognostic factor in patients with NPC treated with IMRT. However, classification according to the site of invasion has prognostic value. Therefore, patients with various subclassifications of stage T3 disease may receive treatment with different intensities; however, further studies are warranted to prove this.

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The encouraging effects of HER2-ADC in patients with HER2-low expression cancers indicated the classical classifications based on positive and negative HER2 might no longer be suitable. However, the biology and prognosis of colorectal cancer patients with different HER2 expression status were still not clear. This is a multi-center retrospective study that included patients with histologically confirmed colorectal cancer and determined HER2 status who received radical surgical resection. HER2 immunohistochemistry (IHC) 1+ and IHC 2+ groups were combined and defined as a HER2-low group because of the concordance of clinicopathological characteristics. As compared with the HER2-high group, both the HER2-zero and the HER2-low group had less tumor with perineural invasion (14.3%, 13.1% vs. 31.6%, p = 0.001 and p < 0.001), less stage III disease (41.8%, 39.9% vs. 56.1%, p = 0.044 and p = 0.022), more RAS/BRAF mutation (52.1%, 49.9% vs. 19.5%, p < 0.001 and p < 0.001) and better disease-free survival (DFS) (3y-DFS rate of 78.7%, 82.4% vs. 59.3%, p < 0.001 and p < 0.001). Multivariate analysis and propensity score matching also revealed that HER2-high expression was an independent prognostic factor of DFS. In conclusion, our study revealed that HER2-low colorectal cancer tumors are close to HER2-zero tumors, but different from HER2-high tumors. The routine examination of HER2 IHC is needed in early-stage colorectal cancer.

e15628 Background: Fluorouracil -based neoadjuvant chemoradiotherapy(CRT) followed by total mesorectal excision and adjuvant chemotherapy is the standard treatment for locally advanced rectal cancer (LARC). Adjvuant FOLFOX improved survival benefit compared with fluorouracil in patients with ypStage II andIII after CRT. However, induction or consolidation chemotherapy with FOLFOX before surgery had been the new standard for LARC. Whether adjuvant chemotherapy with FOLFOX still improves survival outcomes in ypStage III patients previously exposed to oxaliplatin-based treatment was unknwon. Methods: Patients with LARC receiving oxaliplatin-based neoadjuvant treatment from January 2015 to December 2019 were retrospective analyzed. The inclusion criteria included neoadjuvant FOLFOX chemotherapy alone or induction chemotherpay, concurrent FOLFOX and consolidation chemotherapy before CRT. The duration of neoadjuvant oxaliplatin exposure time was less than 4 months. The efficacy of adjvuant FOLFOX chemotherapy was analyzed among these ypStage III patients according to adjuvant chemotherapy cycles after surgery. Results: A total of 227 patients with ypStage III were enrolled, with the 3-year DFS rate of 46.1% (95%Cl 37.3%-54.9%).Among these patients, 193 patients received adjuvant FOLFOX chemotherapy, including 7 patients had ≤ 2 cycles of adjuvant treatment. And 34 patients had observation after surgery. The 3-year DFS rates bewteen FOXFOL adjvuant chemotherapy group and observation group were 44.7% vs. 56.5%, respectively (HR, 1.190, 95%Cl 0.6246-2.267, P = 0.597). Forty-one patients had ≤ 2 cycles of adjuvant treatment. The 3-year DFS was 43.6% vs. 60.4% (P = 0.597) between pateints receiving over 2 cycles of adjvuant chemotherapy and ≤ 2 cycles of treatment. Conclusions: Among ypStage III LARC pateints after neoadjuvant treatment with Oxaliplatin-Based regimen, adjuvant chemotherapy with FOLFOX failed to improved surival benefit. More enhanced regimen might be necessary for these oxalipatin-resistant patients.

head) to 1.11 (rectum) for the composite plan and from 1.00 to 1.27 for individual treatment beams. For the thorax, estimates of the tumor RBE ranged from 1.05 to 1.06; composite plan RBE estimates for OARs (heart, lungs, spinal cord, esophagus, breast, brachial plexus) ranged from 1.02 (breast) to 1.2 (spinal cord). Biological hot spots (RBE up to 1.27) were noted to arise near the distal edge of the Bragg peak. Conclusion: Patient-and tumor-specific RBE estimates from a model that accounts for spatial variations in LET are within +5% of a constant clinical RBE of 1.1. Estimates of the RBE among patients can differ from 1.1 by as much at 15% (RBE w 1.0 to 1.3) for some OAR. The OAR RBE values for individual beams can differ substantially from the RBE for the composite plan, which suggests that beam by beam optimization of (variable RBE x dose) might be exploited to reduce treatment complications (reduce the OAR RBE from w 1.3 to 1.0). This could potentially allow room to increase the therapeutic ratio by 10% to 20% of the total treatment dose.