Expression of P-glycoprotein and metallothionein in gastrointestinal stromal tumor and leiomyosarcomas. Clinical implications

Exp ession o P-glycop o ein and Me allo hionein in Gas oin es inal S omal Tumo and Leiomyosa comas. Clinical Implica ions So ia PÉREZ-GUTIÉRREZ,1Rica do GONZÁLEZ-CÁMPORA,2Joaquín AMÉRIGO-NAVARRO,3 An onio BEATO-MORENO,4Ma ía SÁNCHEZ-LEÓN,2Ma ía Jesús PAREJA MEGÍA,2 Juan An onio VIRIZUELA-ECHABURU,5An onio LÓPEZ-BELTRÁN6 1Pa hology Se ice, Juan Ramón Jiménez Hospi al, Huel a; 2Depa men o Pa hology, Vi gen Maca ena Uni e si y Hospi al and Uni e si y o Se ille Medical School, Se ille; 3Pa hology Se ice, Hospi al To ecá denas, Alme ía; 4Depa men o S a is ic and Ope a ions Resea ch, Uni e si y o Se ille, Se ille; 5Oncology Se ice, Vi gen Maca ena Uni e si y Hospi al, Se ille; 6Depa men o Pa hology, Reina So ia Uni e si y Hospi al and Có doba Uni e si y Medical School, Có doba, Spain ARTICLE © 2007 A ányi Lajos Founda ion PATHOLOGY ONCOLOGY RESEARCH Vol 13, No 3, 2007 A icle is a ailable online a h p://www.webio.hu/po /2007/13/3/0203 In oduc ion Gas oin es inal s omal umo s (GIST) a e neoplasms o igina ing om in e s i ial cells o Cajal (ICC) o hei p ecu so ,9and accoun o 1-3% o malignancies in he Recei ed: Oc 17, 2006; accep ed: July 10, 2007 Co espondence: P o . Rica do GONZÁLEZ-CÁMPORA, Depa - men o Pa hology, Vi gen Maca ena Uni e si y Hospi al, A da, D . Fed iani s/n, 41009 Se ille, Spain. Tel: 34 955008556, Fax: 34 954371284, e-mail: [email p o ec ed] We in es iga ed he exp ession o P-glycop o ein (P-GP) and me allo hionein (MT) in a se ies o 92 GIST and 14 gas oin es inal leiomyosa comas (GI- LMS) wi h he pu pose o expand ou knowledge on he biological bases o GIST chemo- esis ance and o asce ain hei signi icance in pa ien s’ p og- nosis. P-GP exp ession was mo e equen in GIST han in GI-LMS (83.7% s. 21.4%, p<0.001), wi h no di e ence be ween low- and high- isk GIST (p=1.000) o low- and high-g ade GI-LMS (p=0.538). P-GP exp ession was un ela ed o ana omic loca- ion (gas ic s. in es inal) in GIST (39/45 s. 35/43, p=0.770) and in GI-LMS (0/2 s. 2/6, p=1.000). MT exp ession was non-signi ican ly highe in GI-LMS han in GIST (35.7% s. 14.1%, p=0.060), wi h no di e ence be ween low- and high- isk GIST (p=1.000) o low- and high-g ade GI-LMS (p=1.000). MT exp ession was un ela ed o he ana omic loca- ion (gas ic s. in es inal) in GIST (7/45 s. 6/43) and GI-LMS (0/2 s. 1/6) (p=1.000 and p=0.1000, espec i ely). O e all umo -speci ic su i al (p< 0.001) and disease- ee su i al (p<0.001) we e di - e en in GIST as compa ed wi h GI-LMS, and he numbe o e en s was highe in GI-LMS. When he su i al analysis ook in o conside a ion P-GP o MT exp ession, he o e all su i al in GIST was in luenced by he exp ession o MT (p=0.021) bu no by ha o P-GP (p=0.638). Howe e , in GI-LMS, P-GP exp ession in luenced disease- ee su i al (p=0.050); in addi ion, i is impo an o ecognize he limi ed alue o hese esul s because o he low numbe o cases in ol ed in he s udy. Di e en ial exp ession o P-GP and MT migh explain he known a iabili y in esponse o sys emic chemo he apy in hese umo s. De ec ion o P-GP and MT seems o add ce ain p ognos ic alue in GIST (MT) o GI-LMS (P-GP). (Pa hology Oncology Resea ch Vol 13, No 3, 203–208) Key wo ds: gas oin es inal s omal umo s, GIST, leiomyosa comas, P-glycop o ein, me allo hionein gas oin es inal ac (GI).1Un il 1998, when Hi o a e al10 and Kindblom e al13 demons a ed ha GIST a e a special g oup o GI mesenchymal umo s cha ac e ized by CD117 exp ession and equen KIT mu a ion, mos o hese neo- plasms we e conside ed leiomyosa comas (LMS), we e ea ed wi h chemo he apy and had low esponse a e. This chemo- esponse con as ed wi h hose epo ed in LMS in o he loca ions whe e he esponse a e was sig- ni ican ly highe .3The biological bases o chemo-sensi i - i y o hese neoplasms emain unce ain, bu i is well known ha an h acyclines and cispla in, d ugs used in ad anced LMS and GIST, a e he subs a e o mul i-d ug esis ance (MDR) p o eins15 and me allo hionein (MT),12 espec i ely. On he o he hand, since he in oduc ion o he apeu ic a ge ing wi h y osine kinase inhibi o ima inib (Glee ec, No a is Pha ma AG, Basel, Swi ze land) o GIST ea - men ,11 special e o has been made o sepa a e his umo s om hei mimic y, and specially om LMS, which has e y low- o-null esponse o ima inib,14 which is in i o also a subs a e o MDR.7 Ou pu pose is o es ablish whe he o no he exp es- sion o he MDR p o eins, pa icula ly P-glycop o ein (P- GP) and me allo hionein (MT) may co ela e o he pa ien s’ ou come and i addi ionally migh assis o explain he obse ed di e ences in esponse o sys emic chemo he apy in a se ies o GIST and gas oin es inal LMS (GI-LMS). Ma e ial and me hods Pa ien s The s udy g oup included 106 pa ien s wi h GIST (n=92) o GI-LMS (n=14) e ie ed om 3 hospi als in Sou he n Spain. Pa ien s’ ollow-up was a ailable in 77 cases (64 GIST and 12 GI-LMS) and was calcula ed as he numbe o mon hs om he da e o he su gical p ocedu e o he las isi o dea h. The o e all umo -speci ic su i al was de ined as he ime be ween diagnosis and he pa ien ’s dea h. The disease- ee su i al was de ined as he ime be ween he diagnosis and he i s elapse o he appea - ance o me as ases. Cance - ela ed dea h was de ined as ha caused by he umo . Pa hology GIST umo s we e g ouped in o wo p ognos ic ca e- go ies esul ing om g ouping he ou ca ego ies o igi- nally p oposed by Fle che e al5wi h he addi ion o an “o e ly malignan g oup”:16 low (65: 3 e y low isk, 42 low isk, 20 in e medium isk) and high (27: 26 high isk, 1 o e ly malignan wi h me as asis). LMS20 we e g aded as low (n=8) and high (n= 6). In o de o de e mine i he exp ession o P-GP o MT in GI-LMS is egion-depen- den , an addi ional g oup o 26 non-GI LMS om he u e us (12), e ope i oneum (8), skin and so issues (6) was e alua ed. Addi ional immunohis ochemical ma ke s (CD117, CD34, smoo h muscle ac in, desmin and S-100) we e included o con i m pa hologic diagnosis in GIST and LMS. A ailable hema oxylin and eosin s ained slides we e e- assessed by h ee pa hologis s (SGP, RGC, ALB) blind o he clinical s a us. Fo immunohis ochemis y, a ep e- sen a i e pa a in block om each umo , selec ed based on he amoun o umo p esen , was se ially cu a 4 µm hick, depa a inized in xylene, ehyd a ed in g aded e hanol and washed o 5 min wi h phospha e-bu e ed saline. Fo an igen e ie al, he sec ions we e boiled imme sed in 10 mM ci a e bu e (pH 6.0). To a oid non- speci ic CD117 immunos aining, we ollowed he manu- ac u e ecommenda ions and he p ocedu e included wi h Ta ge Re ie al Solu ion (S1699, Dako, Glos up, Denma k). Endogenous pe oxidase was blocked by incu- ba ion o he slides o 30 minu es wi h 3% hyd ogen pe - oxide in me hanol. Sec ions we e hen incuba ed wi h he p ima y mouse monoclonal an ibodies a oom empe a- u e (Table 1). Immunohis ochemis y was pe o med using he high- ly sensi i e polyme -based sys em (EnVision, Dako) 30 min a oom empe a u e wi h diaminobenzidine ch o- mogen subs a e solu ion (0.6 mg/ml in T is-bu e ed saline, pH 7.6, wi h 12 ml 30% hyd ogen pe oxide). Sec- ions we e coun e s ained wi h Maye ’s hema oxylin, dehyd a ed and moun ed ollowing s anda d p ocedu e. Th ee pa hologis s (SGP, RGC, ALB) independen ly e alua ed all immunos ainings in a blinded ashion. The ollowing s aining pa e ns we e conside ed: CD117, cy oplasmic and/o memb ane; CD34, memb ane; smoo h muscle ac in and desmin, cy oplasmic; S-100, cy oplasmic and nuclea ; P-GP, memb ane and some- imes also cy oplasmic; MT, cy oplasmic and nuclea . Cases wi h less han 10% posi i e cells we e conside ed nega i e. 204 PÉREZ-GUTIÉRREZ e al PATHOLOGY ONCOLOGY RESEARCH Table 1. P ima y an ibodies used in he assessmen o GIST and GI-LMS P ima y an ibodies Clone Wo king dilu ion Sou ce Con ols CD117 (c-ki ) 104D2 1:50 Dako mas cells CD34 AM236-5M p edilu ed Biogenex endo helial cells Smoo h muscle ac in 1A4 p edilu ed Dako muscle laye om in es inal wall Desmin D33 p edilu ed Dako muscle laye om in es inal wall S-100 p o ein AM058-5M p edilu ed Biogenex Schwann cells om no mal in es inal wall Me allo hionein E9 1:200 Dako mamma y gland P170/P-glycop o ein C494 p edilu ed LabVision Co co ical ad enal gland MDR Ab-5 S a is ical analysis Bi a ia e analysis o compa e p ognos ic ca ego ies and he exp ession o P-GP and MT we e unde aken by Fishe es and chi-squa e analysis. Uni a i- a e su i al analysis o P-GP and MT exp essions was con- duc ed using Kaplan-Meie me hod and di e ences among g oups we e es ed by log- ank es . All s a is ical analyses we e pe o med using he SPSS o Windows So wa e (SPSS Inc, Chicago, IL, USA). A p- alue o less han 0.05 was conside ed as signi ican . Resul s Table 2 shows ele an com- pa a i e da a on GIST and GI- LMS cases included in his s udy. Plasma memb ane and some- imes cy oplasmic exp ession o P-GP was obse ed in GIST (83.7%) and GI-LMS (21.4%) (p<0.001) (Fig. 1a,b). No di e - ences we e ound be ween low- and high- isk GIST (p=1.000) o low- and high-g ade GI-LMS (p=0.538). In he same way, P- GP exp ession was un ela ed o ana omic loca ion (gas ic s. in es inal) in GIST (39/45 s. 35/43, p=0.770), in bo h low- (p=0.447) and high- isk g oups (p=0.355), and in GI-LMS (0/2 s. 2/7, p=1.000). MT was de ec ed in sca e ed umo cells in he cy oplasm and occasionally in he nucleus (Fig. 1c,d) in GI-LMS (35.7%) and GIST (14.1%) (p=0.060). No di e ences we e obse ed be ween low- and high- isk GIST (p=1.000) o low- and high-g ade GI-LMS (p=1.000). No associa ion was ound be ween MT exp ession and ana omical loca- ion (gas ic s. in es inal) in GIST (7/45 s. 6/43) o GI- LMS (0/2 s.1/6) (bo h p=1.000). Simul aneous P-GP and MT exp ession was obse ed in 11/92 GIST and 1/14 GI- LMS cases (p=1.000). O e all umo -speci ic su i al and disease- ee su - i al we e di e en in GIST as compa ed wi h GI-LMS (bo h p<0.001); he numbe o e en s was highe in GI- LMS (Table 3). When he s udy was es ic ed o high- isk GIST and all GI-LMS, no signi ican di e ences we e obse ed in o e all o disease- ee su i al (p=0.081 and p=0.373, espec i ely). When he su i al analysis ook in o conside a ion P-GP o MT exp ession, he o e all su i al in GIST was in luenced by he exp ession o MT (p=0.021) bu no by P-GP (p=0.638). On he o he hand, P-GP exp ession signi ican ly in lu- enced disease- ee su i al in GI-LMS (p=0.050) (Table 3); howe e , i is impo an o ecognize he limi ed alue o hese esul s because o he low numbe o cases in ol ed in he s udy. No di e ences we e obse ed 205 P-glycop o ein and Me allo hionein in GIST and Leiomyosa comas Vol 13, No 3, 2007 Table 2. Clinical, pa hological da a and ma ke exp ession in 92 cases o GIST as compa ed wi h 14 GI-LMS cases GIST (n=92) GI-LMS (n=14) Age (yea s) Mean 61.44 70.83 Median 64.00 74.50 Sex Male 49 (53.3%) 4 (28.6%) Female 43 (46.7%) 10 (71.4%) Loca ion S omach 45 (48.9%) 2 (14.3%) Small bowel 38 (41.3%) 5 (35.7%) La ge bowel 5 (5.4%) 2 (14.3%) Mesen e y-omen um 4 (4.3%) 5 (35.7%) Size (cm) Mean 6.85 8.28 Median 5.00 9.00 Cell ype Spindle 66 (71.7%) 14 (100%) Epi helioid 22 (23.9%) – Mixed 4 (4.3%) – Risk/g ade ca ego y Low 65 (70.7%) 8 (57.1%) High 27 (29.3%) 6 (42.9%) Make immuno eac i i y P-glycop o ein 77 (83.7%) 3 (21.4%) Low- isk: 58 (89.2%) Low-g ade: 1 (12.5%) High- isk: 19 (70.4%) High-g ade: 2 (33.3%) Me allo hionein 13 (14.1%) 5 (35.7%) Low- isk: 8 (12.3%) Low-g ade: 3 (37.5%) High- isk: 5 (18.5%) High-g ade: 2 (33.3%) Clinical ollow-up n=64 (69.5%) n=13 (86.6%) Low- isk: 43 (67.2%) Low-g ade: 8 (61.5%) High- isk: 21(32.8%) High-g ade: 5 (38.5%) Mean (mon hs) 66.48 32.08 Median (mon hs) 36.00 23.50 Tumo ecu ence 10 (15.6%) 4 (33.3%) Me as ases 8 (12.5%) 6 (50%) Ali e wi h disease 11 (17.2%) 2 (16.7%) Ali e wi hou disease 41 (64.0%) 3 (25.0%) Dead o disease 8 (12.5%) 7 (58.3%) Dead o o he causes 4 (6.2%) 0 (0%) be ween GI-LMS and non-GI LMS o P-GP (p=0.199) o MT exp ession (p=0.979). Discussion Se e al d ug esis ance p o- eins ha e been conside ed as he sou ce o explaining chemo-sen- si i i y in malignan umo s. Two o he mos ex ensi ely s udied p o eins a e P-GP and MT. P-GP is a ansmemb ane p o ein, encoded by he MDR1 gene, which ac s as an e lux anspo e sys em o a a ie y o o ganic subs ances, including cy o oxic d ugs, like an h acy- clines, Vinca alkaloids and epipodophyllo oxins.15 MT is a low-molecula -weigh cys ein- ich enzyme ha binds di alen 206 PÉREZ-GUTIÉRREZ e al PATHOLOGY ONCOLOGY RESEARCH Table 3. O e all and disease- ee su i al o pa ien s wi h GIST and GI-LMS acco ding o P-glycop o ein and me allo hionein exp ession O e all Disease- ee su i al p- alue su i al p- alue GIST P-glycop o ein P-glycop o ein – + – + 1/12 7/52 p=0.638 4/12 15/52 p=0.692 Me allo hionein Me allo hionein – + – + 5/56 3/8 p=0.021 16/56 3/8 p=0.571 GI-LMS P-glycop o ein P-glycop o ein – + – + 7/10 0/2 p=0.066 8/10 1/2 p=0.050 Me allo hionein Me allo hionein – + – + 3/7 4/5 p=0.258 4/7 5/5 p=0.210 GIST s. GI-LMS 8/64 s.7/12 p<0.001 19/64 s. 9/12 p<0.001 Da a a e p esen ed as numbe o e en s / case numbe in he g oups wi h nega i e o posi i e exp ession o he ma ke s Figu e 1. Gas oin es inal s omal umo . Posi i e immuno eac ion o P-GP, 20x (a) and MT, 40x (b). Gas oin es inal leiomyosa - coma. Posi i e immuno eac ion o P-GP, 40x (c) and MT, 20x (d) ab cd me al ions and plays a p o ec i e ole agains an icance d ugs, such as cispla in.4,12 I is well known ha GIST is mo e chemo- esis an han LMS,3,14,18 bu li le is known on he subjacen mechanism. Plaa e al18 s udied he exp ession o P-GP, MRP1 and LRP in 29 pa ien s wi h so issue LMS and 26 pa ien s wi h a p ima y malignan GIST, and ound ha P-GP and MRP1 exp essions we e signi ican ly highe in GIST han in LMS, and ha pa ien s wi h LMS had a be e o e all su i al and a me as a ic pa e n di e en om GIST. Mo e ecen ly, Theou e al19 in es iga ed he exp ession o MDR p o eins (P-GP, MRP1 and BCRP) by Wes e n blo ing in 21 GIST cases, showing P-GP and MRP1 in 86% and 62%, espec i ely, and nega i i y o BCRP. These au ho s ound signi ican di e ences in P-GP exp ession be ween gas ic and non- gas ic umo s. In addi ion, hey sugges ed ha MDR p o- eins do no impai he ini ial esponse o he umo o ima- inib, since none o he six pa ien s ea ed wi h ima inib was esis an . In he p esen se ies we ha e ound simila esul s ega ding P-GP, showing signi ican di e ences be ween GIST and GI-LMS. On he o he hand, GI-LMS had a wo se o e all (p<0.001) and disease- ee (p=0.001) su - i al han GIST, bu when only high- isk GIST en e ed he analysis, no di e ences we e ound. This inding, which di e s om ha epo ed by Plaa e al,18 may be ela ed o Plaa ’s selec ion c i e ia since hey included high- isk GIST only, 68% o which exp essed c-ki . In his se ies we could no con i m he di e en P-GP exp ession be ween gas ic and in es inal cases, since 39/45 o gas ic and 35/43 o non-gas ic neoplasms exp essed P-GP. None o ou pa ien s we e ea ed wi h ima inib. MT exp ession is known as an ad e se p ognos ic ac o in some umo s, including sa comas2bu , as a as we know, his is he i s epo ela ing i s exp ession wi h su i al in GIST. We ha e ound no signi ican di e ences be ween GI-LMS (35.7%) and GIST (14.1%) (p=0.060), bu in GIST, MT exp ession was associa ed wi h o e all cance -speci ic su i al (p=0.021). Ou esul s in GI-LMS ag ee wi h hose o Gaumann e al6whe e MT exp ession in LMS was un ela ed o he pa ien s’ su i al. We did no ind any di e ences in he P-GP and MT exp ession be ween GI-LMS and non-GI LMS, a inding ha may help o explain ha he lowe esponse a e o con en ional chemo he apy, obse ed in p e ious GI- LMS se ies,3could be ela ed o misclassi ica ion o umo s a he han hei loca ion. None heless, chemo- esis ance is a complex phenomenon whe e o he d ug esis ance21 and/o an i-apop o ic mechanisms ela ed o KIT o PDGFRA o e exp ession a e implica ed.8,17 In GIST, ima inib esis ance seems o be ela ed o KIT o PDGFRA mu a ions a he han o MDR p o eins sys- ems, since some speci ic mu a ions cause a low o null esponse.8 In conclusion, di e ences in P-GP and MT exp ession could help o explain he obse ed esponse o sys emic chemo he apy in GIST and LMS. Immunoexp ession o P- GP and MT may assis in di e en ia ing GIST and GI- LMS in selec ed cases, and seems o and ce ain p ognos- ic alue in GIST (MT) and GI-LMS (P-GP). Re e ences 1. Be man J, O´Lea y TJ: Gas oin es inal s omal umo wo k- shop. Hum Pa hol 32:578-582, 2001. 2. Dziegiel P, Salwa-Zu awska W, Zu awski J, Wojna A, Zabel M: P ognos ic signi icance o augmen ed me allo hionein (MT) exp ession co ela ed wi h Ki-67 an igen exp ession in selec ed so issue sa comas. His ol His opa hol 2: 83-89, 2005. 3. Edmonson JH, Ma ks RS, Buckne JC, Mahoney MR: Con as o esponse o daca bazine, mi omycin, doxo ubicin and cis- pla in (DMAP) plus GM-CSF be ween pa ien s wi h ad anced malignan gas oin es inal s omal umo s and pa ien s wi h o he ad anced leiomyosa comas. Cance In es 20:605-612, 2002. 4. End esen L, Bakka A, Rugs ad HE: Inc eased esis ance o chlo ambucil in cul u ed cells wi h a high concen a ion o cy oplasmic me allo hionein. 43: 2918-2926, 1983. 5. Fle che CMD, Be man JJ, Co less C, Go s ein F, Laso a J, Longley BJ, Mie inen M, O'Lea y TJ, Remo i H, Rubin BP, Shmookle B, Sobin LH, Weiss SW: Diagnosis o gas oin es i- nal s omal umo s: a consensus app oach. Hum Pa hol 33: 459-465, 2002. 6. Gaumann A, Tews DS, Men zel T, Pe ow PK, Maye E, O o M, Ki kpa ick CJ, K iegsmann J: Exp ession o d ug esis ance ela ed p o eins in sa comas o he pulmona y a e y and poo - ly di e en ia ed leiomyosa comas o o he o igin. Vi chows A ch 442: 529-537, 2003. 7. Hegedus T, O i L, Sep odi A, Va adi A, Sa kadi B, Ke i G: In e ac ion o y osine kinase inhibi o s wi h he human mul- id ug anspo e p o eins, MDR1 and MRP1. Biochim Bio- phys Ac a 1587: 318-325, 2002. 8. Hein ich MC, Co less CL, Deme i GD, Blanke CD, on Meh en M, Joensuu H, McG ee ey LS, Chen CJ, Van den Abbeele AD, D uke BJ, Kiese B, Eisenbe g B, Robe s PJ, Singe S, Fle che CD, Silbe man S, Dimi ije ic S, Fle che JA: Kinase mu a ions and ima inib esponse in pa ien s wi h me as a ic gas oin es inal s omal umo s. J Clin Oncol 21:4342-4349, 2003. 9. Hi o a S, Isozaki K: Pa hology o gas oin es inal s omal umo s. Pa hol In 56:1-9, 2006. 10. Hi o a S, Isozaki K, Mo iyama Y, Hashimo o K, Nishida T, Ishigu o S, Kawano K, Hanada M, Ku a a A, Takeda M, Muhammad Tunio G, Ma suzawa Y, Kanaku a Y, Shinomu a Y, Ki amu a Y: Gain-o - unc ion mu a ions o c-ki in human gas- oin es inal s omal umo s. Science 279: 577-580, 1998. 11. Joensuu H, Robe s PJ, Sa lomo-Rikala M Ande sson LC, Te - aha iala P, Tu eson D, Silbe man S, Capde ille R, Dimi ije- ic S, D uke B, Deme i GD: E ec o he y osine kinase inhibi o STI571 in a pa ien wi h me as a ic gas oin es inal s omal umo s. N Engl J Med 344:1052-1056, 2001. 12. Kagi JHR: O e iew o me allo hionein. Me hods Enzymol 205: 613-626, 1991. 13. Kindblom LG, Remo i HE, Aldenbo g F, Meis-Kindblom JM: Gas oin es inal pacemake cell umo (GIPACT): gas oin es i- nal s omal umo s show pheno ypic cha ac e is ics o he in e - s i ial cells o Cajal. Am J Pa hol 152:1259-1269, 1998. 207 P-glycop o ein and Me allo hionein in GIST and Leiomyosa comas Vol 13, No 3, 2007 14. Lehne T: Gas oin es inal sa coma (GIST) – a e iew o su - gical managemen . Ann Chi Gynecol 87: 297-305, 1998. 15. Me ino V, Rele ance o mul id ug esis ance p o eins on he clinical e icacy o cance he apy. 1: 203-212, 2004. 16. Nilsson B, Bumming P, Meis-Kindblom JM, Oden A, Do ok A, Gus a sson B, Sablinska K, Kindblom LG: Gas oin es inal s omal umo s: he incidence, p e alence, clinical cou se, and p ognos ica ion in he p eima inib mesyla e e a – a popula- ion-based s udy in wes e n Sweden. Cance 103: 821-829, 2005. 17. Ning ZQ, Li J, A ceci RJ: Ac i a ing mu a ion o c-ki a codon 816 con e s d ug esis ance in human leukemia cells. Leuk Lymphoma. 41: 513-522, 2001. 18. Plaa BEC, Hollema H, Willemina MM: So issue leiomyosa - comas and malignan gas oin es inal s omal umo s: di e - ences in clinical ou come and exp ession o mul id ug esis- ance p o eins. J Clin Oncol 18: 3211-3220, 2000. 19. Theou N, Gil S, De ocelle A Julie C,La e gne-Slo e A, Beauche A, Calla d P, Fa ino i R, Le Cesne A, Lemoine A, Fai e-Bon- homme L, Emile JF: Mul id ug esis ance p o eins in gas oin- es inal s omal umo s: si e-dependen exp ession and ini ial esponse o ima inib. Clin Cance Res 11: 7593-7598, 2005. 20. Weiss SW, Goldblum JR: Enzinge and Weiss´s so issue umo s, 4 h ed., Mosby, S . Louis, 2001. 21. Zwelling A, Slo ak ML, Do oshow JH, Hinds M, Chan D, Pa k- e E, Mayes J, Sie KL, Mel ze PS, T en JM: HT1080/DR4: A P-Glycop o ein-nega i e human ib osa coma cell line exhibi - ing esis ance o opoisome ase II- eac i e d ugs despi e he p esence o a d ug sensi i e opoisome ase II. J Na l Cance Ins 82: 1553-1561, 1990. 208 PÉREZ-GUTIÉRREZ e al PATHOLOGY ONCOLOGY RESEARCH Rep oducedwi hpe missiono hecopy igh owne .Fu he ep oduc ionp ohibi edwi hou pe mission.