More than 90% of biliary tract malignancies are adenocarcinomas. In patients with BTC, the median overall survival (OS) is approximately 12 months with current standard-of-care first-line therapy.² This decreases to approximately 6 months in the second-line setting.

Subtypes of BTC include intrahepatic cholangiocarcinoma, extrahepatic cholangiocarcinoma, and gallbladder cancer. Intrahepatic cholangiocarcinoma originates within the liver, and often, patients present with incidental hepatic lesion(s). Risk factors for intrahepatic cholangiocarcinoma include primary sclerosing cholangitis, cirrhosis, obesity, diabetes, and chronic hepatitis B and C.⁴ Patients with extrahepatic cholangiocarcinoma typically present with obstructive jaundice. The risk factors for extrahepatic cholangiocarcinoma include primary sclerosing cholangitis, gallstones, and Lynch syndrome. Gallbladder cancer is often an incidental finding following cholecystectomy for localized disease, although patients with advanced-stage disease usually present with abdominal pain.

Molecular profiling of tissue samples by next-generation sequencing, immunostaining procedures, or polymerase chain reaction is very important in the care of patients with BTC because it is a molecularly heterogeneous disease. Comprehensive molecular profiling is recommended by the National Comprehensive Cancer Network (NCCN) for patients with unresectable or metastatic BTC who are eligible for systemic therapy to determine the presence or absence of actionable molecular alterations.⁵

FGFR fusions or rearrangements and IDH1 mutations are the most frequently occurring genetic alterations in intrahepatic cholangiocarcinoma with an incidence of approximately 10% to 20%. In other subtypes of BTC, however, these alterations are rare. Among patients with cholangiocarcinoma or gallbladder cancer, HER2 amplification or overexpression has been reported in approximately 5% to 30% of cases. Other molecular alterations that have been reported in BTC cases and recommended by the NCCN for molecular testing include NTRK fusion (<1%), RET fusion (<1%), BRAF V600E mutation (1%-5%) and KRAS G12C mutation (1%). Of interest and significant importance, effective drugs targeting these molecular alterations have been developed in recent times.

However, obtaining a sufficient sample size for molecular characterization can be difficult because of the small tissue samples available after biopsies and because of the high incidence of tissue necrosis. As a result, cell‑free DNA assessment has become a popular alternative for evaluating BTC when the initial biopsy yields insufficient tumor tissue or when an additional biopsy is contraindicated for various other reasons.

Most of the genetic alterations in BTC can be detected with high frequency using cell‑free DNA analysis, an attractive and alternative approach for cancer genomic profiling that can overcome many of the limitations of  tissue-based assays. For the detection of FGFR2 fusions, however, it was reported that the use of cell-free DNA lacks sufficient sensitivity for accurate detection compared with analysis using tissue samples.⁶

In the past decade, numerous treatments have emerged for patients with advanced BTC. These treatments can be categorized into 3 main groups: cytotoxic chemotherapy, immunotherapy, and targeted therapy. Available chemotherapeutic options in the advanced-stage setting include gemcitabine plus cisplatin, leucovorin/5-fluorouracil/oxaliplatin (FOLFOX), leucovorin/fluorouracil/irinotecan (FOLFIRI), and nanoliposomal irinotecan in combination with 5-fluorouracil (5-FU). Immunotherapy-based options primarily include the combination of immune checkpoint inhibitors with cytotoxic chemotherapy.

In addition, there are several available targeted agents directed at biomarkers such as IDH1, BRAF, HER2, NTRK, and KRAS. More recently, agents targeting MDM2 are in clinical development for patients with BTC.

The pivotal, multicenter, randomized phase III ABC‑02 trial investigated gemcitabine alone or in combination with cisplatin for treatment-naive patients with advanced cholangiocarcinoma, gallbladder cancer, and ampullary cancer.⁷  The addition of cisplatin to gemcitabine demonstrated a significant therapeutic advantage with an approximately 36% improvement in OS and a 37% improvement in progression-free survival (PFS) compared with gemcitabine alone (P <.001).

Building on the combination regimen of gemcitabine plus cisplatin, the multicenter, randomized, double-blind phase III TOPAZ‑1 trial investigated the addition of durvalumab, an immune checkpoint inhibitor, to gemcitabine and cisplatin for patients with unresectable, locally advanced or metastatic BTC in the upfront setting.⁸ Patients with recurrent disease more than 6 months after curative surgery and adjuvant therapy were also eligible to participate in the trial. Those randomized to the experimental arm received gemcitabine and cisplatin plus durvalumab followed by durvalumab alone. On the other hand, patients on the control arm received gemcitabine and cisplatin in combination with placebo followed by placebo alone. The primary endpoint was OS and the secondary endpoints included PFS and safety.

The results indicated an OS advantage for the combination of durvalumab with gemcitabine and cisplatin, with a median OS of 12.8 months vs 11.5 months with placebo plus gemcitabine and cisplatin (HR: 0.80; 95% CI: 0.66-0.97; P = .021). Although the median OS showed only a 1.3-month survival advantage, the long-term survival between arms differed significantly. At 24 months, the OS rate was 24.9% with the addition of durvalumab vs 10.4% with gemcitabine and cisplatin alone.

In general, the safety profiles with or without durvalumab were similar with the exception of immune-related adverse events, which occurred in 12.7% of patients who received durvalumab compared with 4.7% of those who received gemcitabine plus cisplatin only.

Based on the results of the TOPAZ-1 trial, the FDA approved durvalumab in combination with gemcitabine and cisplatin for patients with locally advanced or metastatic BTC in September 2022.⁹

The multicenter, randomized, double-blind phase III KEYNOTE‑966 trial has a similar design to the TOPAZ-1 trial. However, in KEYNOTE-966, pembrolizumab was the immune checkpoint inhibitor studied. KEYNOTE-966 randomized patients with previously untreated, unresectable, locally advanced or metastatic BTC to receive gemcitabine and cisplatin in combination with either pembrolizumab or placebo.¹⁰ Patients who had completed (neo)adjuvant therapy within 6 months before diagnosis of advanced disease were also eligible to participate on this trial. The primary endpoint was OS and the key secondary endpoints included PFS, response rate and safety.

The primary endpoint of OS was met.

Pembrolizumab plus gemcitabine and cisplatin demonstrated a statistically significant improvement in OS with a median of 12.7 months compared with placebo plus gemcitabine and cisplatin with a median of 10.9 months (HR: 0.83; 95% CI: 0.72-0.95; P = .0034). The median PFS was 6.5 months with pembrolizumab plus gemcitabine and cisplatin vs 5.6 months with gemcitabine and cisplatin (HR: 0.86; P = .023). However, there was no difference in overall response rates (ORRs) between arms.

Based on the results of this trial, pembrolizumab plus gemcitabine and cisplatin received FDA approval in October 2023 for patients with locally advanced unresectable or metastatic BTC.¹¹

The use of targeted therapy has become a significant area of discussion in BTC, in particular for patients with pretreated disease harboring FGFR fusions/rearrangements. For patients with advanced cholangiocarcinoma, there are already 2 approved FGFR inhibitors: pemigatinib and futibatinib.^12,13

Pemigatinib inhibits FGFR1-3 by noncovalent binding whereas futibatinib inhibits FGFR1-4 via covalent binding. Despite the differences in the mode of binding of these agents, they elicit similar ORRs in patients with unresectable, locally advanced or metastatic cholangiocarcinoma harboring FGFR2 fusions/rearrangements after disease progression on ≥1 prior therapy.^14,15

FGFR inhibitors represent a unique class of targeted agents, specifically in terms of their adverse event profile. Unlike many other drugs used in the treatment of BTC, the most common adverse event associated with FGFR inhibitors is hyperphosphatemia.^16,17 This class of agents is also associated with nail changes and ocular toxicities such as dry eye, keratitis, conjunctivitis, and asymptomatic retinal pigment epithelial detachment. Therefore, it is important for patients receiving FGFR inhibitors to undergo eye examination before treatment ensues, and careful monitoring for phosphorus levels during treatment is needed.

The multicohort, open-label phase I/II ReFocus trial investigated an irreversible FGFR2 inhibitor, RLY‑4008, in patients with unresectable or metastatic cholangiocarcinoma and other solid tumors harboring FGFR2 gene fusion, mutation, or amplification (NCT04526106). RLY‑4008 demonstrated significant antitumor activity with an ORR of 63.2%. Of note, among patients who received the recommended phase II dose of 70 mg/day, the response rate was 88.2%, with 92% of patients achieving tumor size reduction.¹⁸

Tinengotinib is a next-generation FGFR inhibitor. Compared with first-generation FGFR inhibitors that are structurally designed to bind to FGFR2 by reaching into the deeper back pocket of the protein, tinengotinib binds to FGFR2 with high affinity using an active conformation that is structurally designed to bind away from the inner pocket of the protein.^19,20

In a multicohort phase II study for patients with previously treated advanced cholangiocarcinoma, tinengotinib demonstrated an ORR of 40% in the cohort of patients with acquired resistance to a prior FGFR inhibitor. The ORR was approximately 31% among patients with disease harboring other FGFR alterations.²⁰

Based on these positive results, the phase III FIGHT-308 trial is investigating the safety and efficacy tinengotinib vs physician’s choice of treatment (including FOLFOX and FOLFIRI) in patients with FGFR-altered relapsed/refractory cholangiocarcinoma who have previously received ≥1 chemotherapy regimen and 1 FDA-approved FGFR inhibitor (NCT05948475).

IDH1 and IDH2 mutations also occur in cholangiocarcinoma. Although IDH mutations are observed in approximately 20% of intrahepatic cholangiocarcinoma, they rarely occur in extrahepatic cholangiocarcinoma.^21,22

The randomized, double-blind phase III ClarIDHy trial investigated ivosidenib, an IDH1 inhibitor, vs placebo for patients with IDH1 mutation–positive cholangiocarcinoma who had received 1-2 prior therapies including ≥1 gemcitabine or 5-FU–containing regimens.^14,23 The primary endpoint was PFS by blinded independent review committee.

The median PFS was 2.7 months with ivosidenib vs 1.4 months with placebo (HR: 0.37; 95% CI: 0.25-0.54; P <.0001).¹⁴ Although the median PFS was only marginally different by 1.3 months, it is important to note the differences in the PFS rates at 6 and 12 months. For the patients on the placebo arm, all had experienced disease progression before the 6-month time frame. For patients on the ivosidenib arm, however, the 6-month PFS rate was 32% and the 12-month PFS rate was 22%.

Based on these results, ivosidenib received FDA approval for patients with previously treated, locally advanced or metastatic cholangiocarcinoma harboring an IDH1 mutation as detected by an FDA-approved test.²⁴

LY3410738 is a dual IDH1/2 inhibitor that is currently under investigation for patients with cholangiocarcinoma. In a phase I dose-escalation trial, LY3410738 in combination with gemcitabine and cisplatin demonstrated an ORR of 46% among patients with untreated IDH-mutant cholangiocarcinoma.²⁵ At a median follow-up of 4.1 months, the median PFS had not been reached.

BRAF V600E mutations are also seen in BTC. The phase II ROAR study investigated the combination of dabrafenib and trametinib in patients with  unresectable, advanced or recurrent BTC after previous systemic therapy. Dabrafenib plus trametinib demonstrated an ORR of 47%, a median PFS of 9 months by investigator assessment, and a median OS of 13 months in this setting.²⁶ These results are impressive. At the time of reporting, treatment was still ongoing for many of the patients on the trial.

Dabrafenib in combination with trametinib is approved by the FDA for the treatment of patients aged 6 years or older with unresectable or metastatic solid tumors with BRAF V600E mutation who have progressed following prior treatment and have no satisfactory alternative treatment options.²⁷

Trastuzumab deruxtecan is an antibody–drug conjugate directed at HER2.^28,29  Very recently, it gained significant interest in BTC.

Two pivotal studies, HERB and DESTINY Pan-Tumor02 trials, have investigated trastuzumab deruxtecan in previously treated HER2‑expressing advanced BTC.^30,31 Among patients with HER2-positive BTC on either of these trials, the ORR was >36%, the median PFS was >5 months, and the median OS was >7 months. Of note, however, interstitial lung disease is an adverse event of special interest associated with trastuzumab deruxtecan.

Trastuzumab deruxtecan is now approved by the FDA for adult patients with unresectable or metastatic HER2-positive solid tumors who have received prior systemic treatment and have no satisfactory alternative treatment options.³²

Zanidatamab is an investigational HER2-targeted bispecific antibody that binds 2 separate HER2 epitopes, resulting in multiple mechanisms of action.^33,34 In the open-label phase IIb HERIZON-BTC-01 trial, zanidatamab demonstrated significant activity in patients with HER2-amplified locally advanced unresectable or metastatic BTC with disease progression on a gemcitabine‑containing chemotherapy regimen. The ORR was 41.3%, and the median PFS was 5.5 months.^33,35 The most frequent grade ≥3 adverse events reported were diarrhea and decreased ejection fraction, and either of these events occurred in <5% of the patients.

Based on the encouraging results obtained in HERIZON-BTC-01, zanidatamab is now being studied in the multicenter, open-label, randomized phase III HERIZON-BTC-302 trial for patients with HER2-positive advanced BTC who have received ≤2 prior cycles of systemic therapy for advanced disease (NCT06282575). HERIZON-BTC-302 is investigating zanidatamab plus gemcitabine and cisplatin with or without durvalumab or pembrolizumab vs gemcitabine plus cisplatin with or without durvalumab or pembrolizumab. The primary endpoint is PFS in patients with HER2-positive BTC.

Another investigational therapeutic approach in BTC involves the dual targeting of HER2 with the use of tucatinib in combination with trastuzumab. In the multicohort phase II basket trial (SGNTUC-019), this combination demonstrated an ORR of 46.7% and a disease control rate of 76.7% in a cohort of 30 patients with unresectable locally advanced or metastatic HER2-overexpressed or HER2-amplified BTC after ≥1 prior systemic therapy for advanced disease.³⁶ These patients had no prior exposure to any HER2-targeted treatment. In this patient cohort, the median PFS was 5.5 months and the median OS was 15.5 months.

KRAS alterations have been reported in up to 18% of BTC cases.³⁷ KRAS G12C mutations may occur in approximately 1% of patients with cholangiocarcinoma.³⁸ As a result, this driver gene is a potential target in BTC. In fact, the NCCN guidelines recommend testing for the KRAS G12C mutation in patients with BTC.

Adagrasib is an orally available small molecule covalent inhibitor of KRAS G12C. It is being investigated in the phase I/II KRYSTAL‑1 trial for patients with unresectable or metastatic solid tumors harboring a KRAS G12C mutation, and for whom there are no remaining standard-of-care treatment options (NCT03785249).

Among the 12 evaluable patients with BTC, the ORR was 41.7%, and the disease control rate was 91.7%. The median OS was 15.1 months, and the median PFS was 8.6 months.^38,39 

It is clear from all these datasets using targeted therapies that precision oncology is critical for the optimal management of patients with advanced BTC. Most of the breakthroughs and approvals of targeted therapies in BTC have emerged during the past 7 years.^{[2,5,17,26,40]} Since 2017, the field has seen significant progress and this has resulted in the approval of multiple targeted treatment options for patients with BTC. The treatment landscape continues to expand, and it is becoming increasingly clear that early molecular profiling is important upfront and post disease progression for the identification of potential targeted therapies for this patient population, including enrollment on appropriate clinical trials for potential patient benefit.

Despite these recent advances, there continues to be unmet clinical needs in the care of patients with BTC. With continued technological improvements and increasing assay sensitivities, several new targetable biomarkers are being discovered. Newly emerging strategies showing potential for efficacy include targeting the MDM2/p53 signaling pathway.

MDM2 and p53 are 2 important driver genes in BTC.³⁷  In a study using samples from 160 patients with intrahepatic cholangiocarcinoma (n = 109), extrahepatic cholangiocarcinoma (n = 40), and gallbladder cancer (n = 11), transcriptomic sequencing showed that the primary form of MDM2 alteration in BTC is MDM2 amplification, which was reported in approximately 5% of cases. In this study, the identified p53 gene alterations included frameshift indel, in-frame indel, identical and nonidentical missense, and splice site mutations, accounting for approximately 26% of the cases.

Alterations in several other driver genes were also reported in this study including alterations in KRAS (18%) and MYC amplification (5%).

MDM2 is an E3 ubiquitin ligase and p53 is an important tumor suppressor gene because when its expression is altered, either via mutations or loss, it can promote the development and growth of cancer cells. Of significant importance, MDM2 amplifications and p53 mutations are mostly mutually exclusive.³⁷  However, since MDM2 is a negative regulator of p53, alterations in the MDM2 gene can potentially lead to increased tumor development and tumor growth. Therefore, the MDM2/p53 signaling pathway has recently attracted attention in BTC, and therefore, drugs targeting MDM2 preventing p53 suppression are currently in development. Today, inhibiting MDM2/p53 signaling in tumors harboring wild-type p53 represents a potential novel therapeutic strategy in BTC.

The efficacy and safety of brigimadlin in advanced solid tumors harboring wild-type p53 is being investigated in 2 pivotal phase I/II clinical trials either as monotherapy (NCT03449381) or in combination with the anti–PD-1 monoclonal antibody ezabenlimab (NCT03964233).^42,43 As of October 2023, 23 patients with BTC were enrolled on both trials, 16 of whom received brigimadlin monotherapy and 7 received brigimadlin in combination with ezabenlimab.⁴⁴  

Among the 12 evaluable patients in the monotherapy arm, 4 achieved a partial response and 6 achieved stable disease. Among the 7 evaluable patients in the combination arm, 4 achieved a partial response and the remaining 3 patients achieved stable disease.

Many of the patients experienced therapeutic benefits lasting for >100 days.⁴¹ For some patients, benefit from the treatment lasted for >200 days, and for some patients, the duration of stable disease lasted for >120 days. At the time of data analysis, treatment was ongoing for patients on the monotherapy and combination arms.

Like all targeted therapies, there are unique class-specific adverse events. Thrombocytopenia and neutropenia were the most frequently observed grade ≥3 treatment-related adverse events associated with brigimadlin with and/or without ezabenlimab. These hematologic adverse events were easily managed by dose reductions and treatment delays as appropriate.

Other adverse events associated with brigimadlin monotherapy or in combination with ezabenlimab included nausea, vomiting, diarrhea, fatigue, decreased appetite, and dysgeusia.

Brightline‑2 is an open-label, single-arm phase II trial that is investigating brigimadlin monotherapy for the treatment of patients with locally advanced or metastatic, MDM2-amplified, p53 wild-type biliary tract adenocarcinoma, pancreatic ductal adenocarcinoma, or other selected solid tumors (NCT05512377). To be eligible for enrollment on this trial, patients must have received all available conventional therapies known to confer clinical benefit. Patients receive oral brigimadlin 45 mg once every 3 weeks until disease progression, unacceptable toxicity or consent withdrawal.

The primary endpoint is ORR, and the secondary endpoints include duration of response, disease control rate, PFS, OS, safety and quality of life.