FAPI therapy — theranostics for the cancers nobody else can target.

What is FAPI therapy?

The therapy is administered as an outpatient intravenous infusion every 6 to 8 weeks for 2 to 4 cycles. Three radionuclide options are available depending on cancer type and disease pattern: Lu-177 FAPI (beta, the standard choice), Y-90 FAPI (high-energy beta, for bulky disease), and Ac-225 FAPI (alpha, for very aggressive or refractory cases).

FAPI therapy is not yet a regulator-approved standard of care — it remains an emerging investigational treatment under compassionate use protocols for patients who have exhausted standard-of-care options. Eligibility is reviewed case by case after a 68Ga-FAPI PET scan confirms strong tracer uptake in the patient's specific disease.

The stromal target — why FAPI is pan-cancer.

Most prior theranostic targets are markers on the cancer cell itself — PSMA on prostate cancer cells, somatostatin receptors on neuroendocrine cells. FAPI targets a completely different compartment: the cancer-associated fibroblasts (CAFs) that populate the tumour's connective-tissue stroma. These fibroblasts surround and support the cancer cells, providing growth signals, immune protection, and metabolic infrastructure.

Fibroblast activation protein (FAP) is selectively expressed on these activated tumour stromal cells — and is almost absent in healthy adult tissues. The therapy exploits this in three steps:

• Binding. A small-molecule FAP inhibitor (FAPI-46 is the most-used variant) is designed to fit precisely into the active site of fibroblast activation protein and bind with high affinity.
• Radiopayload delivery. The FAPI ligand is chemically chelated to a therapeutic radioisotope — Lu-177, Y-90, or Ac-225 — and infused intravenously. The molecule circulates briefly, binds FAP wherever it's expressed, and accumulates intensely in tumour stroma.
• Cytotoxicity. The radioisotope emits radiation that damages DNA in both the bound fibroblasts and the surrounding cancer cells via the cross-fire effect. The result: tumour cell death by both direct hit and bystander mechanism.

Because FAP is expressed across nearly all solid tumour types — not just one cancer — the same FAPI molecule can treat sarcoma in one patient, pancreatic cancer in the next, and breast cancer in a third. One platform, many indications.

Cancers FAPI can treat.

Stromal FAP expression has been documented across more than 28 different cancer types in published literature. Where evidence is strongest — either through prospective trials or published cohort series — we offer FAPI therapy at our centre:

Eligibility for any specific patient is determined by a 68Ga-FAPI PET scan showing strong tracer uptake (typically SUVmax > 8) in the patient's disease. Patients with low or absent FAPI-PET uptake are unlikely to respond to FAPI therapy, and we counsel against offering treatment in those cases.

FAPI PET before therapy.

FAPI therapy never starts without a FAPI PET scan first. The diagnostic version (68Ga-FAPI-46) confirms the molecular target is present, in what quantity, and where the disease is — making FAPI an authentic theranostic pair, not an empirical chemotherapy.

Three radioisotope options.

The same FAPI ligand can be paired with three different therapeutic radionuclides. Choice is driven by tumour size, disease pattern, prior treatment response, and renal/marrow function.

Most patients at our centre start with Lu-177 FAPI as the first line. Y-90 FAPI is preferred where the dominant disease is a single bulky mass. Ac-225 FAPI is reserved for highly selected refractory cases — the evidence base is still preliminary.

The treatment cycle.

FAPI therapy follows a standardised protocol adapted from the Heidelberg and AIIMS published series:

Total course duration: approximately 4 to 7 months for a 2–4 cycle protocol. Each cycle is a same-day outpatient procedure; international patients typically combine each cycle with a 2–3 night stay in Gurugram.

What the literature shows.

FAPI therapy has no phase 3 trial yet. The evidence base is built on prospective and retrospective cohorts from Heidelberg (Germany), Essen (Germany), AIIMS (India) and other major theranostic centres. The signal across these is consistent: meaningful disease control in heavily pre-treated patients with no remaining standard options.

Heidelberg first-in-human series

The Heidelberg group, led by Kratochwil and Lindner, published the first-in-human FAPI-PET imaging series¹ in 2019, demonstrating high tracer uptake across 28 different cancer types. Therapy data followed in 2020–2022, with phase 1 dosimetry and safety data published for both Lu-177 FAPI and Y-90 FAPI^5,6.

Y-90 FAPI in advanced sarcoma

Fendler and colleagues published the Essen experience⁵ with 90Y-FAPI-46 in patients with advanced sarcoma and other refractory solid tumours. The trial documented an acceptable safety profile and disease control in approximately 30–50% of patients, with meaningful symptomatic and biomarker improvements in the responders.

AIIMS Indian first-in-human

Ballal and Yadav at AIIMS Delhi reported the first-in-human results⁷ with Lu-177 DOTA.SA.FAPi and Lu-177 DOTAGA.(SA.FAPi)₂ — long-lived FAPI variants designed for improved tumour retention. The AIIMS series has since grown to include patients across pancreatic, breast, gastric and hepatic cancers.

Real-world response pattern

Across published cohorts, the consistent pattern: disease control rates of 40–60% in heavily pre-treated patients, with the highest response in pancreatic adenocarcinoma, sarcoma, and cholangiocarcinoma. Patients with FAPI-PET SUVmax greater than 10 respond more reliably than those with weaker uptake.

Cost of FAPI therapy in India.

Indicative cycle pricing. Because FAPI therapy is individualised by isotope, dose, and total course, a written quote follows pre-treatment evaluation.

Side effects — generally mild.

FAPI therapy is among the better-tolerated systemic cancer treatments in modern oncology. Because FAP is not strongly expressed in salivary glands, FAPI does not cause the xerostomia (dry mouth) that complicates Lu-PSMA and Ac-PSMA therapy — a meaningful quality-of-life advantage.

Common (>15% of patients)

• Fatigue — mild to moderate, typically 1–2 weeks after each cycle.
• Mild nausea — usually controlled with pre-medication.
• Transient cytopenia — mild reductions in haemoglobin, platelets, lymphocytes.
• Mild transaminitis — brief liver enzyme elevation.

Uncommon (1–15%)

• Bone-marrow suppression — more pronounced in patients with prior heavy chemotherapy or marrow disease.
• Mild renal effects — transient creatinine rise; reversible.
• Mild diarrhoea or appetite loss.

Rare but possible

• Severe myelosuppression — in <3% of patients, typically those with extensive marrow disease.
• Delayed kidney effects — very rare at standard doses; monitored between cycles.

Who is a candidate?

FAPI therapy at our centre is offered under compassionate use protocols. Eligibility is determined case by case after multidisciplinary tumour board review. Standard criteria:

• Histologically confirmed advanced or metastatic solid tumour — one of the FAPI-responsive cancer types listed above.
• Progression on or intolerance to standard-of-care therapy — including prior chemotherapy, targeted therapy where applicable, and immunotherapy.
• FAPI-PET positive disease demonstrated on 68Ga-FAPI-46 PET/CT, with SUVmax greater than the institutional threshold (typically > 8 to 10).
• Adequate organ function: creatinine clearance > 50 mL/min, haemoglobin > 9 g/dL, platelets > 100 × 10⁹/L, AST/ALT < 3× upper limit.
• Life expectancy > 3 months and ECOG performance status 0–2.
• Multidisciplinary tumour board recommendation and informed consent regarding the investigational nature of therapy.

Next available FAPI slots.

FAPI therapy at our centre is scheduled on alternate Fridays, depending on isotope availability and patient demand. Reservations require 7 days advance notice for isotope procurement.