At diagnosis, more than half of pancreatic cancer patients have distant metastasis, and 37%-41.9% have liver metastasis[16, 17]. The first-line chemotherapy regimens recommended by NCCN guidelines are AG or FOLIRINOX. Emerging immunotherapy or targeted therapy has not significantly improved OS and is only effective for patients with specific genetic variants[18, 19]. Overall, there have been no significant improvements in treatment for these patients. It is necessary to stratify patients and develop more active and reasonable treatment plans. When metastases are limited to a single and the most common organ (liver), local therapies should be strengthened based on systemic chemotherapy. Radiotherapy is one of the important local treatments and is expected to achieve good therapeutic effects.
Chemoradiotherapy is the preferred treatment for locally advanced pancreatic cancer, but there are few studies in patients with hepatic oligometastasis. The study found that only 3.6% of patients received radiotherapy, indicating a low percentage. A retrospective study of 34 and 55 patients treated with chemoradiotherapy and chemotherapy, respectively, showed that chemoradiotherapy did not improve OS in all cases. However, subgroup analysis indicated that it prolonged OS in patients with primary tumors located in the pancreas head or good performance status[13]. Another study of 41 patients showed that oligometastatic pancreatic cancer may benefit from stereotactic body radiotherapy[20]. Our large sample study shows that radiotherapy can significantly prolong survival. After PSM, the effect of radiotherapy was still obvious. Radiotherapy is expected not only to eliminate local lesions but also to activate the immune system to kill metastatic tumor cells through radiation-induced bystander effects[21]. SBRT has been reported to induce immune-related cell death in pancreatic cancer in both preclinical models and tissue samples from patients[22, 23]. To provide credible evidence and promote individualized treatment, a prognostic nomogram of liver metastatic PC treated with radiotherapy was established. As we know, no relevant study has been published to date.
Of all the variables included in the analysis, age, race, histology, N staging, primary site surgery, and chemotherapy were factors influencing prognosis. In our study, The CSS was found to be significantly lower in patients aged 70 years and above compared to younger patients. Similar results can be seen in previous studies[24, 25]. Elderly patients often have poor physical fitness, cannot tolerate treatment, and suffer from other conditions. Blacks are associated with a poorer prognosis than other races. This may be due to economic, cultural background, and genetic differences. Histology was a strong predictor of survival in both univariate and multivariate analyses. Pancreatic ductal adenocarcinoma is the most common pathological type, including adenocarcinoma and infiltrating duct carcinoma in the SEER database, showing poor prognosis. The incidence of neuroendocrine carcinoma has risen in recent years and now accounts for approximately 5% of all pancreatic tumors, making it the second most common mass [26, 27]. Neuroendocrine carcinoma and other rare pathological types of tumors have a better prognosis. For the primary tumor site, Leah K Winer et al found that for patients undergoing surgery, tumors in the head of the pancreas had higher resectability but worse OS compared to other sites [28]. But in our research, the primary tumor site does not affect prognosis. Furthermore, T staging is not a prognostic factor. This reveals that primary tumor conditions, such as tumor site, volume, and extent of invasion of surrounding tissue may have no effect affect the prognosis of patients with radiotherapy. However, the survival of patients treated with radiotherapy is shorter when lymph node metastases are present, probably because such patients are more likely to develop distant metastases and the role of radiotherapy is limited.
Surgery exhibited the strongest impact on prognosis. The previous concept holds that pancreatic cancer with liver metastasis is a surgical contraindication. However, in recent years, numerous studies [29–32] have confirmed that surgery in patients with hepatic oligometastatic pancreatic cancer is beneficial for long-term survival in the case of height selection. In the future, we expect high-level clinical evidence to guide the selection of appropriate surgical candidates and update guidelines similar to those for liver metastasis in colorectal cancer. As we expected, patients treated with chemotherapy benefited more than those who did not receive chemotherapy. In the phase III PRODIGE trial, patients with Eastern Cooperative Oncology Group (ECOG) performance status score of 1 or lower were treated with FOLFIRINOX, and the mOS was 11.1 months[33]. Another phase III trial(MPACT) compared the efficacy of gemcitabine + albumin-bound paclitaxel and gemcitabine monotherapy in patients with Karnofsky performance status score ≥ 70%. The OS of the combination group was improved ( 8.7 months vs 6.6 months; HR = 0.72 ; p < 0.0001 ) [34]. Therefore, some patients with an ECOG status score of 2 may be suitable for this combination therapy. In general, systemic chemotherapy is a necessary treatment for patients at this stage.
However, this study has some shortcomings:(1) As a retrospective study, there may be inevitably bias. (2) The SEER database cannot provide detailed radiotherapy information, including the extent of radiotherapy, radiotherapy technology, and dose. Based on clinical experience, we recommend radiotherapy for all malignant tumor sites whenever possible. Otherwise, large-scale and multicenter prospective studies are expected to guide radiotherapy strategies, prove our results, and eliminate the bias.