Usefulness of immunohistochemically determined epidermal growth factor receptor mutations in lung cancer

Namen Preučiti zanesljivost imunohistokemične (IHK) metode za določanje najpogostejših aktivirajočih mutacij v genu za receptor za epidermalni rastni dejavnik (EGFR) pri nedrobnoceličnem raku pljuč (NDRP) v primerjavi s standardno metodo verižne reakcije s polimerazo (PCR) ter napovedno vrednost IHK EGFR pozitivnih mutacij na izhode zdravljenja z zaviralci tirozin kinaz (TKI), usmerjenimi proti EGFR. Dodatno smo želeli preučiti še stroškovno učinkovitost IHK testiranja EGFR mutacij pred PCR testiranjem. Utemeljitev Aktivirajoče EGFR mutacije predstavljajo pozitiven napovedni dejavnik za zelo dober, okrog 70 % odgovor na zdravljenje z EGFR TKI pri bolnikih z razsejanim NDRP in jih standardno določamo s PCR metodo. Senzitivnost PCR metode omejuje delež tumorskih celic z EGFR mutacijo. Poleg tega je PCR testiranje relativno drago, kompleksno, zahteva usposobljen kader, analiza rezultatov pa razmeroma dolgotrajna. IHK metoda določanja specifičnih mutiranih EGFR proteinov z uporabo za pogosti mutaciji specifičnih protiteles, omogoča določitev EGFR mutacij v zelo majhnih tumorjev ali celo le tumorskih celic na enostavnejši, hitrejši, cenejši in dostopnejši način. V literaturi so dostopni podatki o zelo visoki, v povprečju okrog 90 % specifičnosti IHK metode za določanje pogostih EGFR mutacij, medtem ko je bila senzitivnost precej nižja in med posameznimi raziskavami močno spremenljiva, od 30 – 100 %. Podatki o napovedni vrednosti IHK določenih EGFR mutacij so v doslej objavljeni literaturi pičli. Bolniki in Metode V raziskavo smo vključili 79 EGFR mutacije pozitivnih in 29 EGFR mutacije negativnih bolnikov z NDRP, diagnosticiranih po principu refleksnega testiranja z metodo PCR. Za IHK testiranje smo uporabili za mutacije specifični protitelesi proti najpogostejši deleciji v eksonu 19, E746-A750del (klon SP111) in proti točkovni mutaciji L8585R (klon SP125). Reakcijo smo izvedli na avtomatskem barvalniku. 60 od 79 EGFR mutacije pozitivnih bolnikov je bilo zdravljenih z EGFR TKI za razsejano bolezen in so bili vključeni v analizo preživetja. Za oceno stroškovne učinkovitosti smo uporabili odločitveno drevo. &#8195Rezultati Celokupna senzitivnost in specifičnost IHK metode v primerjavi s PCR metodo sta bili 84,8 % (95 % interval zaupanja (CI) 74,6-91,6) in 100 % (95 % CI 85,4-100). Srednji čas brez napredovanja bolezni (PFS) in celokupno preživetje (OS) bolnikov, ki so bili IHK EGFR pozitivni sta bila visoko primerljiva s PFS in OS celotne kohorte PCR EGFR pozitivnih bolnikov (PFS: 14,3 vs. 14,0 mesOS: 34,4 vs. 34,4 mes). Razmerje stroškov PCR in IHK metode bi moralo znašati 8:1 za belo populacijo, oziroma 4:1 za Azijsko populacijo, da bi bilo IHK testiranje pred PCR testiranjem stroškovno učinkovito. Zaključek V naši raziskavi smo potrdili zelo visoko specifičnost in relativno nizko senzitivnost IHK metode za določanje dveh najpogostejših aktivirajočih EGFR mutacij z uporabo specifičnih protiteles. Potrdili smo tudi zanesljivost IHK metode za napoved odgovora na zdravljenje s TKI. Na stroškovno upravičenost IHK testiranja pred PCR testiranjem v največji meri vpliva delež EGFR mutacij v določeni populaciji.Purpose To evaluate the accuracy of immunohistochemistry (IHC) method compared to standard PCR-based method for detecting common activating epidermal growth factor receptor (EGFR) mutations in non-small-cell lung cancer (NSCLC) and to evaluate predictive value of IHC EGFR mutation-positive status for EGFR TKIs treatment outcome. Additionally, based on the results of our study we wanted to evaluate estimated cost-effectiveness for the upfront IHC testing. Background Activating EGFR mutations are predictive for excellent, approximately 70%, response rate for treatment with EGFR TKIs in patients with advanced NSCLC. Standard method for EGFR mutation detection is PCR method. The sensitivity of PCR method is limited by the amount of tumor cells in the tumor specimen. PCR-based EGFR mutation testing is relatively costly, technically comlex, labour demanding, and has relatively long turn-around-times. IHC method using mutant selective antibodies for detection of specific mutant EGFR proteins enables EGFR mutation analysis in small tumor tissue samples or even tumor cells. IHC is easy to conduct, cheaper, widely available and yields fast results. Previously, IHC EGFR mutation detection with mutation specific EGFR antibodies was studies, revealing very high specificity, around 90%, while sensitivity was limited and variable between studies, ranging 30 % - 100 %. Data on predictive value of IHC determined EGFR mutations on response to EGFR TKI are scarce in the available literature. Patients and Methods The trial included 79 consecutive EGFR mutation-positive and 29 EGFR mutation-negative NSCLC cases diagnosed with reflex PCR-based testing. Two mutation-specific antibodies against the most common exon 19 deletion, namely E746-A750del (clone SP111) and L858R mutation (clone SP125) were tested using automated immunostainer. 60/79 EGFR mutation-positive cases were treated with EGFR TKIs for advanced disease and included in treatment outcome analysis. Decision tree was used for the cost-effectiveness analysis. Results The overall sensitivity and specificity of IHC-based method compared to the PCR-based one were 84.8 % (95 % CI 75.6–91.6) and 100 % (95 % CI 85.4–100), respectively. The median PFS and OS of patients with IHC positive EGFR mutation status were highly comparable to the total cohort (PFS: 14.3 vs 14.0 monthsOS: 34.4 vs 34.4 months). The PCR and IHC cost ratio needs to be about eight-to-one and four-to-one in Caucasian and Asian population, respectively, to economically justify upfront use of IHC. Conclusion The trial confirmed an excellent specificity with fairly good sensitivity of IHC with mutation-specific antibodies for common EGFR mutations and the accuracy of IHC testing for predicting response to EGFR TKIs. The use of upfront IHC depends mainly on the population EGFR mutation positivity probability