The anti-aggregating effect of acetylsalicylic acid (ASA 100 mg/day and 200 mg/day) was monitored in platelets of 351 solid tumor patients. As ASA increases the aggregation time, its anti-aggregating effect plays an important role in the prevention of thrombosis. Measurements were performed using the Siemens PFA 100 aggregometer with a collagen/EPI test cartridge. The mean age of patients was 64.33 ± 11.67 years. Among them, there were 74 (21.08%) male and 277 (78.91%) female patients suffering from head and neck tumors - 34 pts (9.69% ), breast cancer - 222 pts (63.2%), lung cancer - 4 pts (1.14%), abdominal cancer - 54 pts (15.4% ), urinary - 4 pts (1.14%), and genital tract cancer - 33 pts (9.4% ). Aggregation levels >160 seconds show the ASA effect on circulating platelets. The anti-aggregating effect of ASA 100 mg/day reported in 142 (40%) pts was absent in 209 (60%) pts. The mean anti-aggregating effect of ASA 100 mg/day for male and female patients was 169.29 ± 79.54 and 168.51 ± 69.71 seconds, respectively. No statistically significant difference was found between the male and female platelet aggregation results (p = 0.759). Interindividual variability in aggregation profiles was observed with the coefficient of variation CV = 41-47%. From the group not responding to ASA 100 mg/day, 40 patients were singled out to receive ASA 200 mg/day; of them 17 (42%) were responsive, and 23 (58%) patients were not responsive. No statistically significant difference was found between the two measurements carried out on samples from the same 38 patients with a 1-month interval (p = 0.063) to show the intraindividual stability of platelet aggregation. Whereas the antiaggregating effect of both ASA 100 mg/day and 200 mg/day has been shown in only 40% patients, dose tailoring based on the individual aggregation result is recommended.Praćen je antiagregacijski učinak acetilsalicilne kiseline (ASK 100 mg/dan i 200 mg/dan) na trombocite 351 bolesnika sa solidnim tumorima. ASK produžuje vrijeme agregacije; pa je njen antiagregacijski učinak važan u prevenciji tromboze. Korišten je agregometar Siemens PFA-100 s kolagenskim/epinefrinskim uloškom. Prosječna dob bolesnika bila je 64;33 ± 11;67 godina. Muškaraca je bilo 74 (21;08%); a žena 277 (78;91%). Bolesnici su bolovali od tumora glave i vrata 34 (9;69% ); dojke 222 (63;2% ); pluća 4 (1;14%); trbuha 54 (15;4% ); mokraćnog 4 (1;14%) i spolnog sustava 33 (9;4%). Vrijednosti agregacije >160 sekundi pokazuju djelovanje ASK na trombocite. Antiagregacijski učinak ASK 100 mg/dan bio je u 142 (40%) bolesnika; a nije ga bilo u 209 (60%). Prosječni antiagregacijski učinak ASK 100mg/dan za muškarce bio je 169;29 ± 79;54 sekundi; a za žene 168;51 ± 69;71 sekundi. Statistički značajne agregacijske razlike izme|u rezultata muškaraca i žena nije bilo (p = 0;759). Interindividualna varijabilnost agregacije pokazuje koeficijent varijabilnosti CV = 41-47%. Iz skupine koja nije reagirala na ASK 100 mg/dan izdvojeno je 40 bolesnika i liječeno primjenom ASK 200 mg/dan. Reagiralo je 17 (42%); a nije 23 (58%). Nije bilo statistički značajne razlike dvaju mjerenja uzoraka 38 istih osoba; u razmaku od mjesec dana (p =0;063); što pokazuje intraindividualnu stabilnost agregacije. S obzirom na to da se samo u 40% osoba uočava antiagregacijski učinak ASK 100 mg/dan i 200 mg/dan; preporučuje se individualno doziranje oslonjeno na agregacijski nalaz
