Inclusion Criteria:
1. Written informed consent and HIPAA authorization for release of personal health information
2. Age ≥ 18 years and ≤ 70 years at the time of consent
3. 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.
4. Performance Status (PS) of ECOG 0-2 at the time of enrollment
5. 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
6. 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.
7. As determined by the enrolling investigator, ability of the participant to understand and comply with study procedures for the entire length of the study
8. Ability to swallow oral medications
Exclusion Criteria:
1. Receiving chemotherapy in adjuvant setting
2. Prior VTE/PE
3. Currently taking anticoagulation or antiplatelet therapy. Non-steroidal anti-inflammatory drug (NSAID) use for pain is allowed
4. Prior indication for anticoagulation or anticoagulation contraindicated (e.g., active bleed or risk of bleeding, such as history of gastrointestinal ulcers)
5. Allergy to ASA
