PBRM and RM-133 are two steroid derivatives recently developed in our research group as anticancer agents. PBRM, or 3-{[(16β,17β)-3-(2-bromoethyl)-17-hydroxyestra-1(10,2,4-trien-16-yl]methyl} benzamide, was synthesized in solution from estrone (E1) using a sequence of eight steps in an overall yield of 11%. The structure was confirmed by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. 2D-NMR experiments, such as HSQC (heteronuclear single-quantum correlation), HMBC (heteronuclear multiple-bond correlation), COSY (correlation spectroscopy) and NOESY (nuclear Overhauser effect spectroscopy), were also needed to identify all protons and carbons. PBRM inactivated the transformation of E1 into estradiol (E2), the most potent estrogen, by the action of steroidogenic enzyme 17β-hydroxysteroid dehydrogenase (17β-HSD) type 1, which is thought to play a pivotal role in the progression of estrogen-sensitive breast cancer. In fact, PBRM inhibited the 17β-HSD1 in T-47D cells (IC50 = 83 nM), the pure enzyme (Ki = 381 nM, kinact = 0.084 min-1) and did not inhibit other key enzymes such as 17β-HSD2, 17β-HSD7, 17β-HSD12, CYP3A4 and CYP-2D6, suggesting a good selective action. When tested in vivo on the T-47D xenograft tumor model in female ovariectomized nude mice, PBRM (250 μg/mouse/day) fully blocked (100%) the tumor growth induced with exogenous E1 (0.1 μg/mouse/day). RM-133, or {4-[(2β,3α,5α,17α)-3,17-dihydroxypregn-20-yn-2-yl]piperazin-1-yl}[(2S)-1-(quinolin-2-ylcarbonyl)pyrrolidin-2-yl]methanone, was synthesized in small quantity in 97% purity by solid-phase synthesis using the new diethylsilylacetylenic linker we have previously developed. It was next synthesized in solution and in larger quantity for in vivo assays starting from androsterone and using a sequence of six steps in an overall yield of 14%. NMR spectroscopy, especially 2D-experiments (HSQC, HMBC, COSY and NOESY), confirmed the right structure and to identify all protons and carbons. The presence of two conformers in proportions that range according to the NMR solvent was also clearly observed. RM-133 has been reported to be a promising pro-apoptotic agent showing antiproliferative activity (IC50 ranging from 0.1 to 4.5 μM) on various human cancer cell lines (HL-60, PANC-1, LNCaP, LAPC-4, MCF-7, T-47D and OVCAR-3). When tested in vivo on the OVCAR-3 xenograft tumor model in female ovariectomized nude mice, RM-133 (6 mg/mouse/day) fully blocked (100%) the tumor growth. In summary, both PBRM and RM-133 steroid derivatives were synthesized, characterized and generated promising in vivo results against breast cancer and ovary cancer tumor models, respectively.