• Written informed consent and HIPAA authorization for release of personal health information

• Age ≥ 18 years and ≤ 70 years at the time of consent

• Histological confirmation of stage IS or IIA or higher testicular or germ cell cancer. Primary mediastinal and retroperitoneal GCT are allowed. Seminoma and non-seminoma histologies are allowed.

• Performance Status (PS) of ECOG 0-2 at the time of enrollment

• At least one of the following high risk of VTE features:

• a. Stage IIC or III or higher per AJCC 8th edition criteria i. Stage IIC - any pT/TX, N3, M0, S0-1 ii. Stage III - any pT/TX, any N, M1, SX iii. Stage IIIA - any pT/TX, any N, M1a, S0-1 iv. Stage IIIB - any pT/TX, N1-3, M0, S2 or any pT/TX, any N, M1a, S2 v. Stage IIIC - any pT/TX, N1-3, M0, S3 or any pT/TX, any N, M1a, S3 or any pT/TX, any N, M1b, any S Serum marker (S category) S criteria SX Marker studies not available or not performed S0 Marker study levels within normal limits S1 LDH \< 1.5 x normal and hCG \< 5000 IU/L and AFP \<1000 ng/mL S2 LDH 1.5 to 10 x normal or hCG 5000 to 50,000 IU/L or AFP 1000 to 10,000 ng/mL S3 LDH \>10 x normal or hCG \>50,000 IU/L or AFP \>10,000 ng/mL

• b. Intermediate or poor risk by IGCCCG criteria i. Intermediate risk - testis/retroperitoneal primary and no non pulmonary visceral metastases plus at least one of the following markers: AFP \> 1,000 ng/mL to ≤ 10,000 ng/mL, beta-hCG \> 5,000 IU/L and ≤ 50,000 IU/L, LDH \>1.5 x normal and ≤ 10 x normal ii. Poor risk - mediastinal primary or non-pulmonary visceral metastases plus at least one of the following markers: AFP \> 10,000 ng/mL, beta- hCG \> 50,000 IU/L, LDH \> 10 x normal c. Khorana score of 2 or higher i. +1 point for testicular/germ cell cancer (All patients will receive +1 for their testicular/germ cell cancer diagnosis. Thus, a patient with any other Khorana characteristic \[ii-v\] will meet this inclusion criteria.) ii. +1 point for platelet ≥350 x 10\^9/L iii. +1 point for hemoglobin \<10 g/dL iv. +1 point for leukocyte count \>11 x 10\^9/L v. +1 point for BMI \>35 kg/m\^2

• Planning or recently started 3-4 cycles of standard of care front-line cisplatin-based chemotherapy (bleomycin, etoposide, and platinum \[BEP\], etoposide and cisplatin \[EP\], or etoposide, ifosfamide, and cisplatin \[VIP\]). Note: ASA should be initiated no later than 2 weeks after initiation of standard front-line chemotherapy.

• As determined by the enrolling investigator, ability of the participant to understand and comply with study procedures for the entire length of the study

• Ability to swallow oral medications