I do not think that depoprovera will mask the symptoms of oavrian cancer.
The main consequnece of depoprovera is not having a period.
emedicine has a good summary. I have pasted it below
Injectable Depomedroxyprogesterone Acetate
DMPA is a suspension of microcrystals of a synthetic progestin that is injected intramuscularly. Pharmacologically active levels are achieved within 24 hours after injection, and serum concentrations of 1 ng/mL are maintained for 3 months. During the fifth or sixth month after injection, the levels decrease to 0.2 ng/mL, and they become undetectable by 7-9 months after injection.
DMPA acts by the inhibition of ovulation with the suppression of follicle-stimulating hormone (FSH) and LH levels and eliminates the LH surge. This results in a relative hypoestrogenic state. Single doses of 150 mg suppress ovulation in most women for as long as 14 weeks. The contraceptive regimen consists of 1 dose every 3 months.
DMPA is an extremely effective contraceptive option. Neither varying weight nor use of concurrent medications has been noted to alter efficacy. Within the first year of use, the failure rate is 0.3%.
DMPA does not produce the serious adverse effects of estrogen, such as thromboembolism. Diminished anemia occurs. Dysmenorrhea is decreased. The risks of endometrial and ovarian cancer are decreased. It contains no estrogen, thus making it suitable for women who cannot or will not take estrogen products. It also is safe for breastfeeding mothers.
Disruption of the menstrual cycle to eventual amenorrhea occurs in 50% of women within the first year. Persistent irregular bleeding can be treated by administering the subsequent dose earlier or by prescribing temporary low-dose estrogen therapy. Because DMPA persists in the body for several months in women who have used it on a long-term basis, it can delay the return to fertility. Approximately 70% of former users desiring pregnancy conceive within 12 months, and 90% of former users conceive within 24 months. Similar to the delay in fertility after discontinuation of DMPA, other adverse effects, such as weight gain, depression, and menstrual irregularities, may continue for as long as 1 year after the last injection.
The FDA issued a "black-box" warning in November 2004, stating that bone loss from using Depo-Provera "may not be completely reversible" even after stopping the drug. The warning urged women not to use Depo-Provera on a long-term basis unless all other methods were inadequate.
Most users of DMPA are teens at a crucial age for the building of bone density; about 10% of American females aged 15-19 years who use birth control use Depo-Provera, compared with 3% of women in the United States overall.
Studies have contradicted the FDA warning. Women who stopped using DMPA experienced an average bone gain of 1.34% at the hip versus a loss of 0.19% for women who never took the drug. Spine density increased 2.86% for women who stopped using the drug, compared with an increase of 1.32% for nonusers. Furthermore, teens regained their bone density faster than older women using Depo-Provera.4
The main limitation, from the patient's point of view, has been the intramuscular (IM) route of injection, which requires an office visit every 12-14 weeks for administration. A subcutaneous version of the drug is now available (depo-subQ provera 104) that delivers a lower dose of medroxyprogesterone acetate (MPA) than does the intramuscular formulation (104 mg vs 150 mg). The subcutaneous route opens the possibility for home self-injections, and the lower dose could decrease suppression of pituitary function and ovarian estradiol production. Further study is needed.