Is incidence for all cancers higher with HRT?

The short version: the evidence here does not answer whether HRT raises incidence of all cancers combined. It only tracks a few specific cancers, and the answer differs by type.

The retrieval covers breast, ovarian, endometrial, colorectal, and CNS tumors, but never adds them up into an all-cancer rate. That is a meaningful gap. A woman on HRT might trade a lower colorectal cancer risk for a higher breast or ovarian cancer risk, and the net effect on total cancer incidence is never reported in these studies.

For breast cancer, the picture is clear. The 2019 Lancet meta-analysis of 58 studies found that combined estrogen-progestin therapy raises breast cancer risk from the first years of use (relative risk 1.6 for 1–4 years) and increases with longer use (RR 2.08 for 5–14 years) [4]. Estrogen-only therapy did not raise risk and may have lowered it slightly in the WHI trial (RR 0.77) [4]. A 2003 imaging study of 300 women found cancer in 8.3% of HRT users versus 3.3% of non-users [3]. The 2007 breast cancer incidence drop in women aged 50–69, coinciding with the WHI announcement that HRT raised breast cancer risk, is consistent with a causal link [2].

For ovarian cancer, a meta-analysis of 36 studies covering 4.2 million participants found a 29% increase in risk with any HRT use (RR 1.29), especially for serous and endometrioid types [4]. For CNS tumors, a UK study found a 21% increase in all CNS tumors (RR 1.21), driven by meningioma and acoustic neuroma [1]. For colorectal cancer, the same review notes a reduced risk, but does not give a number [4].

The missing piece is the all-cause cancer incidence. No study in this retrieval added these risks together. A woman taking combined HRT faces a higher risk of breast, ovarian, and CNS cancers, and a lower risk of colorectal cancer. Whether the total is higher depends on the baseline rates of each cancer, which vary by age and genetics. The WHI trial, the largest randomized source, did report total cancer as a secondary outcome, but that data is not in this retrieval.

My call: the evidence shows HRT raises risk for several common cancers and lowers risk for one, but no study here reports the net all-cancer incidence. The burden of proof has not been met for the claim that HRT is neutral or protective for total cancer. Confidence: moderate for the individual cancer risks, low for the all-cancer question because it was never studied.