• Signed Informed Consent Form

• Age \>= 18 years at time of signing Informed Consent Form

• Ability to comply with the study protocol, in the investigator's judgment

• Histologically or cytologically confirmed colorectal adenocarcinoma, gastric adenocarcinoma, pancreatic adenocarcinoma, hepatocellular carcinoma, or extra-hepatic/intra-hepatic/gallbladder adenocarcinoma. Patients may be enrolled irrespective of any mutational analyses.

• Must have been diagnosed with any stage disease (including localized and metastatic disease) that was felt to have already been treated completely with curative-intent per investigator's, primary physician's, or research team's judgement. Curative-intent treatment strategies are unique to each tumor type and stage but includes all surgeries and perioperative therapies recommended. If patients were appropriately treated with curative intent but felt to be high-risk for relapse, they may be still be included.

• o Patients diagnosed with hepatocellular carcinoma specifically must have Child Pugh A score at the time of screening; o Patients must have completed all definitive SOC treatment with curative intent (neoadjuvant, surgery, radiation, and adjuvant treatments) for specific tumor-type and stage per investigator's/primary physician's or research team's judgment. Curative treatment regimens including chemotherapy, radiation, treatment sequencing, and surgery should have been followed as per local standards and NCCN guidelines or non-standard curative-intent therapy through a clinical trial at the discretion of the investigator/treating physician.

• Patients who have undergone definitive, curative-intent treatment of oligometastatic (synchronous or metachronous) disease with NED per investigator judgement are acceptable for enrollment.

• Must have disease-free status documented by complete physical examination and imaging studies with no evidence of recurrent, residual, or metastatic disease on standard imaging (chest, abdomen, and pelvis captured by CT chest and CT or MRI of abdomen and pelvis) per investigator assessment within 28 days prior to enrollment

• Must have a tumor-specific ctDNA SignateraTM test with a positive result (any mean tumor molecule/mL) drawn within 1 year of completing all curative-intent treatment and within 28 days prior to enrollment. In the setting of a negative scan for recurrence, this will be defined as subclinical molecular disease.

• ECOG Performance Status of 0-2

⁃ Adequate hematologic and end-organ function, defined by the following laboratory test results, obtained within 28 days prior to initiation of study treatment:

∙ ANC ≥1.5 x 109/L (1500/uL) without granulocyte colony-stimulating factor support

‣ Lymphocyte count ≥ 0.5 x 10\^9/L (500/uL)

‣ Platelet count ≥ 75 x 10\^9/L (75,000/uL) without transfusion

‣ Hemoglobin ≥ 90 g/L (9 g/dL) Patients may be transfused to meet this criterion.

‣ AST, ALT, and alkaline phosphatase (ALP) ≤ 3 x upper limit of normal (ULN)

‣ Note: for HCC, AST, ALT, and alkaline phosphatase (ALP) ≤ 5 x upper limit of normal (ULN)

‣ Serum bilirubin ≤ 1.5 x ULN with the following exception: Patients with known Gilbert disease or HCC: serum bilirubin ≤3 x ULN

‣ Serum creatinine ≤ 1.5 x ULN or Creatinine clearance ≥ 50 mL/min (calculated using the Cockcroft-Gault formula)

‣ Urine dipstick for proteinuria \< 2 + (if ≥ 2+ proteinuria on dipstick urinalysis, patient should undergo 24-hour urine collection and must demonstrate \< 1 g protein in 24 hours).

‣ Serum albumin ≥ 25 g/L (2.5 g/dL). Cut-off of ≥ 28 g/L (2.8 g/dL) will be used for HCC patients.

‣ For patients not receiving therapeutic anticoagulation: INR or aPTT ≤ 1.5 x ULN. Note: for HCC patients INR or aPTT should be ≤ 2 x ULN.

⁃ For patients receiving therapeutic anticoagulation: stable anticoagulant regimen

⁃ Negative HIV test at screening, with the following exception: patients with a positive HIV test at screening are eligible provided they are stable on anti-retroviral therapy, have a CD4 count ≥ 200µL, and have an undetectable viral load.

⁃ Select patients with well compensated, treated HBV infection and chronic HCV infection may be considered

⁃ Women of childbearing potential must have a negative serum test result within 28 days prior to initiation of study treatment. If a urine pregnancy test is positive, it must be confirmed by a serum pregnancy test.

⁃ Women must not be breastfeeding.

⁃ For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods, and agreement to refrain from donating eggs as defined below: o Women must remain abstinent or use contraceptive methods with a failure rate of \< 1% per year during the treatment period and for at least 5 months after the final dose of atezolizumab and for 6 months after the last dose of bevacizumab. o Women must refrain from donating eggs during this same period. o A woman is considered to be of childbearing potential if she is postmenarchal, has not reached a postmenopausal state (≥ 12 continuous months of amenorrhea with no identified cause other than menopause), and has not undergone surgical sterilization (removal of ovaries and/or uterus). The definition of childbearing potential may be adapted for alignment with local guidelines or requirements.

⁃ For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and agreement to refrain from donating sperm, as defined below: o With a female partner of childbearing potential who is not pregnant, men who are not surgically sterile must remain abstinent or use a condom plus an additional contraceptive method that together result in a failure rate of \< 1% per year during the treatment period and for 6 months after the final dose of bevacizumab. Men must refrain from donating sperm during this same period. o With a pregnant female partner, men must remain abstinent or use a condom during the treatment period and for 6 months after the final dose of bevacizumab to avoid exposing the embryo. o The reliability of sexual abstinence should be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or postovulation methods) and withdrawal are not adequate methods of contraception.