Unexpected Long-Term Survival in Resected Pancreatic Ductal Adenocarcinoma Harboring KRAS G12D/SMAD4 Co-Mutation: A Case Report and Mini-Review

1. Introduction and Clinical Significance

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers, with an annual death rate approaching incidence. Despite advances in diagnosis and treatment, most cases are detected at advanced stages, when curative surgery is no longer feasible.

In contrast, incidentally detected pancreatic lesions may allow earlier diagnosis and surgical intervention. Resected early-stage PDAC and high-risk pancreatic lesions in asymptomatic individuals are associated with improved survival, compared with patients with symptomatic disease, largely due to smaller tumor burden and higher resectability at diagnosis [1].

Genetically, more than 90% of PDAC cases harbor a KRAS mutation [2], predominantly with codon 12 alterations, KRAS G12D being the most common [3,4]. This variant has previously been associated with more aggressive tumors and worse clinical outcomes in resectable disease prognosis [4,5,6,7,8]. Loss of SMAD4 function is linked to tumor progression and metastatic dissemination and represents an established unfavorable prognostic factor for OS [9,10]. Several studies demonstrated that the combination of KRAS and SMAD4 mutations was an independent prognostic factor for progression-free survival (PFS) and OS, and patients with both KRAS and SMAD4 mutations have significantly shorter PFS and OS than those without this mutational profile [7,8,10,11,12,13].

Importantly, the co-occurrence of KRAS G12D and SMAD4 mutations is defined as an independent predictor of shorter PFS and OS, suggesting the existence of a high-risk molecular subtype of PDAC with limited therapeutic responsiveness to standard chemotherapy.

This article reports a rare case of incidentally detected PDAC harboring a KRAS G12D/SMAD4 co-mutation that achieved a prolonged period of stable disease and OS and presents a narrative review of the literature, emphasizing available treatments and their clinical significance. Beyond genomic alterations, emerging biomarkers such as ccfDNA) and systemic inflammatory markers, including NLR, have shown potential prognostic value in pancreatic cancer, although their clinical utility remains under investigation

2. Case Presentation

A 71-year-old woman with a medical history of hypertension, prior cholecystectomy for gallstone disease, and a family history of rectal adenocarcinoma had a screening computed tomography (CT) colonography in June 2019 that showed a 25 mm mass in the pancreatic body. The tumor was invading and stenosing the portal vein confluence without arterial invasion or adenopathy (Figure 1A).

The patient was admitted to the Gastroenterology Clinic in July 2019. No abnormality was found upon physical examination, and laboratory tests showed normal values of carbohydrate antigen 19-9 (CA19-9), carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP) levels, and total bilirubin. The patient was enrolled in a prospective observational study (PANCNGS: October 2018 – December 20221) after providing informed consent. The study was approved by the institutional review board (IRB: 23878/14.06.2018) and included endoscopic ultrasound (EUS)-guided tissue acquisition and fine needle aspiration (FNA) of the pancreatic mass (Figure 1B) and peripheral blood sampling. EUS-FNA of the pancreatic lesion (Figure 1B) confirmed well-differentiated PDAC (Figure 1C-D).

Genomic DNA (gDNA) and ccfDNA were isolated using the same protocols that we detailed in our prior research [14,15]. The ccfDNA concentration was quantified using a Qubit 3.0 Fluorometer (Life Technologies) and measured in ng/μL, eluted in 25 μL of ultra-pure water, and measured 6.3 ng/mL. The NLR was calculated as the ratio between the peripheral blood neutrophil and lymphocyte counts and was 4.49. Subsequently, targeted amplicon-based next-generation sequencing (NGS) was carried out using the Illumina NextSeq500 platform. NGS analysis revealed a pathogenic mutation in KRAS (G12D), along with alterations in SMAD4, ARID1A, TSC2, TP53, EGFR, and ERBB2 (HER2), identified in FNA or in both FNA and ccfDNA samples (Table 1).

Following multidisciplinary tumor board evaluation, the disease was classified as resectable PDAC, and surgical resection was recommended.

Variants detected at low variant allele frequency (VAF) likely reflect tumor heterogeneity and ultra-deep sequencing sensitivity. Clinical significance of these alterations should be interpreted in the context of longitudinal molecular monitoring.

On July 23, 2019, the patient underwent a distal pancreatectomy with splenectomy and lateral resection of the portal vein. Pathological examination confirmed PDAC (pT2N1Mx, lymphovascular invasion positive, perineural invasion positive, stage IIB, AJCC 8^th edition) [16]. Six days later, the patient developed diffuse abdominal pain and bilious output from the surgical drain. Abdominal CT scan revealed a perforated gastric ulcer with generalized peritonitis (Figure 2A). An emergency surgical re-intervention was performed on July 31, 2019, including segmental gastrectomy, double-layer gastrorrhaphy, peritoneal lavage, and drainage. Four days after the second surgical procedure, the patient presented with severe abdominal pain, and elevated drain fluid lipase (9 993 U/L) and amylase (3 996 U/L) levels significantly increased, consistent with acute pancreatitis of the pancreatic remnant. The supramesocolic accumulation (Figure 2B) was evacuated via laparotomy.

Following postoperative recovery, adjuvant chemotherapy with gemcitabine monotherapy was started in November 2019 due to the patient’s low performance status (ECOG 2-3), and it was continued until April 2020, when the restage CT scan showed progressing disease (Figure 2C, 2D).

Second-line treatment with gemcitabine plus capecitabine was administered from May 2020 to October 2021, achieving stable disease during the initial six cycles. Third-line therapy with nano-liposomal irinotecan (Onivyde®) plus 5-fluorouracil (5-FU) was initiated in December 2021 and continued until August 2022, when disease progression involved the superior mesenteric vein, superior mesenteric artery, and celiac trunk, accompanied by rising CA19-9 (114 U/L) (Figure 2E). In September 2022, fourth-line therapy with mFOLFOX6 was started following a multidisciplinary tumor board discussion. Disease stabilization was maintained until April 2023, when clinical deterioration occurred, accompanied by a marked increase in CA19-9 (555 U/L). Imaging revealed progression of liver metastasis and new peritoneal nodules (Figure 2F). The patient’s condition progressively declined, and she died in November 2023, after a 53-month OS. The patient’s treatment timeline is illustrated in Figure 3.

3. Discussion

Prognostic Value of ccfDNA Concentration and NLR in PDAC

In a previously published prospective cohort study including 82 patients with PDAC, we demonstrated that higher values of NLR (≥ 3.31) were linked with worse OS (4 vs. 10 months; log rank p = 0.011), and an elevated ccfDNA concentration (≥ 25.79 ng/mL) was strongly associated with shorter OS (4 vs. 8 months; log rank p = 0.009). According to the results of the multivariable Cox regression analysis, the baseline concentration of ccfDNA was an independent prognostic factor for OS (HR 0.45, 95% CI 0.21-0.97, p = 0.041). Furthermore, when ccfDNA levels and NLR were combined, patients with both biomarkers negative (ccfDNA concentration < 25.79 ng/ml and NLR < 3.31) showed significantly longer OS than patients with one or both biomarkers positive [14]. In various studies, multivariate analysis demonstrated that patients with higher NLR (cut-off values ranged from 2 to 5) had a worse prognosis than those with lower NLR [17,18,19,20]. This patient had a ccfDNA concentration of less than 25.79 ng/ml and an NLR of less than 5, which may indicate a favorable biological profile.

KRAS G12D/SMAD4 Co-Mutation’s Impact on Chemotherapy Responsiveness and Survival

About 90% of invasive PDACs have KRAS mutations, which appear early in the disease. Although KRAS mutations occur too frequently to be considered appropriate prognostic factors, previous reports mention that the KRAS mutant subtype G12V or G12D is associated with poor prognosis [21]. Several studies reported that the presence of the KRAS G12D in the primary tumor was a negative prognostic factor, including within the subgroup that received chemotherapy [22,23,24,25].

The impact of SMAD4 loss on chemotherapy responsiveness may vary depending on certain treatment regimens and disease stages, even though it is linked to a worse prognosis and shorter survival [9,26,27].

SMAD4 mutations were identified as a predictive factor for relapse-free survival (RFS) out of the four driver genes. Additionally, it was discovered that the combination of SMAD4 and KRAS mutations was an independent predictor of OS and RFS [28].

Nevertheless, SMAD4 deletion significantly accelerated the growth of pancreatic tumors when paired with the carcinogenic KRAS G12D mutation, resulting in a marked decrease in survival [13,29,30]. SMAD4 mutations predict poor response to chemotherapy and are associated with early metastatic spread. Currently not targetable, but may serve as a biomarker for aggressive disease needing intensified monitoring or alternative therapeutic strategies [9,31]. At the moment of the NGS panel, the frequency of SMAD4 mutation was extremely low, but taking into account the aggressive phenotype these mutations generate, it could be highly significant during patient follow-up.

The co-occurrence of KRAS G12D and SMAD4 mutations defines a high-risk molecular subtype, commonly associated with poor prognosis, enhanced metastatic potential, and limited responsiveness to standard chemotherapy [7,8,10,11,12,13]. In a retrospective cohort study, Shen et al. reported that patients with KRAS G12D mutation had inferior survival among those with resectable disease [4]. Similarly, Yokose et al. demonstrated that the combination of KRAS and SMAD4 mutations is an independent poor prognostic factor for recurrence and survival in resected PDAC [11].

Impact of KRAS Mutation Subtypes and Co-Occurring Mutations on Treatment Response and Prognostic

It has been demonstrated that TP53 mutations do not significantly impact prognosis in patients with KRAS G12D mutations [32]. TP53 mutation, frequently observed in PDAC, adds to the aggressive biology, reflecting a high degree of genomic instability and resistance to apoptosis [10,33,34]. Alterations in ARID1A and TSC2 further suggest epigenetic dysregulation and mTOR pathway activation, respectively, both of which are linked to tumor progression and treatment resistance [35,36,37,38].

Although KRAS mutations have long been considered “undruggable”, the recent development of G12D-specific inhibitors (e.g., MRTX1133) opens the door for targeted therapy in clinical trials [31,39,40].

ARID1A mutations are associated with increased tumor immunogenicity, especially when accompanied by high tumor mutational burden or microsatellite instability [36]. The high frequency of occurrence of these mutations in our case may suggest sensitivity to immune checkpoint inhibitors (e.g., anti-PD-1/PD-L1), particularly in the context of a broader immunogenic signature.

ERBB2 (HER2) mutation cases are suitable for HER2-targeted therapy. If confirmed by IHC or FISH as HER2 overexpression or amplification, this may justify the use of HER2-targeted agents (e.g., trastuzumab, pertuzumab, or trastuzumab deruxtecan)[41,42,43,44].

EGFR mutations are of limited significance for PDAC. They require a specific mutational context (e.g., L858R or exon 19 deletion) to be actionable. Historically, EGFR inhibitors (e.g., erlotinib) showed modest benefits in PDAC [45,46]; re-evaluation may be warranted if a sensitizing EGFR mutation is present.

Most variants detected in this case (except KRAS G12D) were identified at low variant allele frequencies (VAFs), likely reflecting the ultra-deep sequencing strategy used. Despite their low abundance, such mutations may hold significant prognostic and therapeutic relevance, particularly when monitored over time. Serial molecular profiling using the same targeted panel may enable early detection of emerging subclones with pathogenic potential or therapy resistance. Thus, these low-frequency variants should not be dismissed, but rather integrated into the longitudinal molecular surveillance strategy for this patient or in similar cases.

Postoperative complications following pancreatic surgery are often associated with treatment delays and the omission of adjuvant chemotherapy [47]. In this case, the patient’s PFS during the first line of chemotherapy (gemcitabine-based regimens) was 18 months, which is comparable to the ESPAC4 trial [48,49]. Under the second line of chemotherapy (Onivyde® +5-FU), the PFS was 9 months (in contrast to the NAPOLI-1 study, where the median PFS was 6.1 months [50]). Additionally, the patient’s tumor marker values were noticeably decreased throughout the second regimen. Notably, treatment was well tolerated despite the patient’s postoperative course.

The incidental diagnosis of an early-stage (resectable) PDAC with KRAS G12D and SMAD4 mutations, which experienced multiple postoperative complications and a prolonged period of stable disease under adjuvant chemotherapy, both on the first and second lines of chemotherapy, exemplifies this case’s uniqueness. Many clinical trials are currently evaluating the safety and effectiveness of KRAS G12D therapy in solid tumors, including PDAC. Enrollment in a trial investigating KRAS G12D inhibitors should be considered if available. However, early diagnosis and surgery remain the cornerstone of increased OS and PFS, even in the presence of negative molecular markers.

4. Conclusions

This case highlights prolonged survival in resected PDAC harboring a KRAS G12D/SMAD4 co-mutation, a molecular profile usually associated with a poor prognosis. Low baseline NLR and ccfDNA levels may have contributed to a more favorable clinical course. Integrating molecular and circulating biomarkers may improve prognostic stratification in resected PDAC.