The tolerability of apatinib, an effective antiangiogenic agent, varies greatly in patients with stage IV cancer during treatment. This study will include patients with advanced (stage IV) gastric cancer, non-small-cell lung cancer (NSCLC), breast cancer or ovarian cancer, who will be administered apatinib treatment starting from 250 mg Qd and closely monitored for ADRs during the period of apatinib treatment. Meanwhile, relevant assay technologies will be used to precisely detect changes of various biomarkers in the patients treated by apatinib, with the aim of identifying biomarkers related to their prognosis and relevant complications so as to screen out the favored population, establish the drug's indication(s) and reduce relevant side effects.

Inclusion Criteria:

1. Age of 18 and over, male or female;

2. Patients with histologically confirmed advanced (stage IV) gastric cancer, NSCLC, breast cancer or ovarian cancer, who choose monotherapy of oral vascular targeting drug (apatinib) due to intolerability or inappropriateness of other therapies;

3. Presence of measurable lesions (≥10mm on spiral CT scan) subject to RECIST 1.1;

4. Blood pressured controlled at 150/100 mHg following drug administration;

5. An ECOG PS score of between 0 and 1;

6. Findings of hematology and laboratory tests at the baseline that meet the following criteria:

   Hemoglobin ≥80g/L; Absolute neutrophil count (ANC) ≥1.5×10^9/L; Platelets ≥90×10^9/L; ALT/AST ≤ 2.5×ULN; or ALT/AST ≤ 5×ULN for patients with hepatic metastases; Serum total bilirubin ≤1.5×ULN; Serum urea nitrogen and creatinine ≤ 1.5×ULN; Serum albumin ≥30g/L; Coagulation function (INR≤1.5, APTT≤1.5 ULN);

7. A life expectancy of at least 3 months;

8. Subjects who volunteer to participate in this study and have signed the Informed Consent Form (ICF), with good compliance with treatment and follow-up.

Exclusion Criteria:

1. Confirmed allergy to apatinin and or its excipients;
2. Hypertension (high blood pressure) that can not be controlled by drugs;
3. A history of active hemorragge, ulcer, intestinal perforation, intestinal obstruction, or major surgery no older than 30 days;
4. NYHA III-IV heart function, or severe hepatic or renal insufficiency (Grade 4);
5. Presence of multiple factors that affect oral medications, such as difficulty swallowing, nausea, vomiting, chronic diarrhea and intestinal obstruction;
6. Pregnant or lactating women, or women of child-bearing potential who have planned a pregnancy, or male and female patients who do not agree to practice adequate contraception during this study;
7. Patients who have a history of psychotropics abuse and can not quit, or who have mental disorders;
8. Participation in other drug clinical trial within the last 4 weeks;
9. Prior therapy with VEGFR inhibitors such as sorafenib and sunitinib;
10. Presence of comorbidities that seriously affect the patient's safety or ability to complete the study, in the investigator's judgment;
11. Patients who can not tolerate apatinib treatment as judged by the investigator depending on the their medical history;
12. Patients that are considered ineligible for this study by the investigator.