Shrug. Both males and females develop about 10 to 15 "potential ducts" shortly after birth (weeks 4 to about 8). At female puberty (or upon HRT), those ducts do start to develop (proliferating the number of alveolar lobes)... but the number of glands does not increase, even in GG females. With the monthly estrous cycles, a GG's breasts mature slowly, reaching Tanner stage 5 (fully mature) by around age twenty... but until she gives birth and lactates, even a GG's breasts has about the same number of mammary ducts as a man — her ducts are just a lot bigger, there are not more of them.

With lactation, however, things change. While the statement that "Estrogen makes the ducts grow and plump up even without producing milk" is also partially true... there is more to that, too. With lactation, not only does the number of lobes (alveoli) increase dramatically, but the number of ducts also increases... typically to around 30 or more, IIRC. With the end of lactation, there is resorption of some of those alveolar lobes (*not* all of them), but the extra glands remain. Which is to say, a woman who has lactated has more of her breast tissue made up of glandular tissue, and less of it is fat. That may make her breasts a little less "perky", but it also means that they do not shrink so much as a nulliparous (never given birth) woman's breasts do when menopause rolls around — or in this case, when HRT is stopped.

As an aside regarding the "Estrogen makes the ducts grow" thing... I do not agree with the conventional wisdom that an estrogen only regimen is as effective as a combined estrogen/progesterone regimen, regarding breast glandular development. Shrug. Breasts grown with straight estrogen may end up as big as those with a combined regimen, but they are more fatty tissue and less glandular development. I usually recommend a progesterone component to HRT... but with the caveat that progesterone is an estrogen antagonist, though, so the usual approach of taking both medications at the same time is rather pointless. And it is worth noting that many doctors routinely prescribe Provera (medroxyprogesterone acatate) rather than a true progesterone. Shrug. Provera works fine for what it was intended for... but it is a synthetic that was deliberately created to mimic only *some* of the properties of progesterone — and the properties they were interested in duplicating had to do with protecting women from endometrial cancer, not breast development. As most TS do not have a uterus to need protection from that form of cancer, Provera is the wrong medication to be taking for breast development HRT... and even if a true progesterone (such as Prometrium) is taken, it should be cycled (stop taking estrogen while taking the progesterone, mimicking a monthly estrous cycle where the estrogen levels drop as the progesterone levels rise during menstruation). Shrug. Most TS are interested in short term results... and there is little short term benefit to that sort of cycling HRT regimen. Indeed, the fact that estrogen is dropped for part of each month (typically one week in four) tends to slow things down a little... so it is not a usual regimen followed, these days. But longer term, the result is better glandular development. Keep in mind that the average GG grows her breasts over the course of five to ten years, not just in six months to a year. But I digress...

Anyway, perhaps of more relevance here is that most TS do not reach Tanner stage 5 breast development. Typically Tanner 3 is reached after 6 months to a year of continuous HRT... and some TS manage to reach Tanner 4 after one to two years. Only rarely is Tanner 5 (full breast maturity) reached in TS who start HRT after the age of twenty or so, due to lower Human Growth Hormone levels when growing breasts as an adult. That means that most TS do not full development of even the 10 to 15 ducts that they started life with... and unless they lactated, they are unlikely to have more ducts than that. Which is to say, their breasts have a higher amount of fatty tissue in them, when compared to a woman with Tanner 5 breasts who has lactated... and hence may "shrink" more when stopping HRT.

Sigh. I suppose I should have mentioned in my earlier reply that I took my first HRT dose in my teens... that I cycle my HRT, and used both true progesterone and human bio-equivalent estrogens while my breasts were still growing... and at one point in my life, I played games with my HRT (as well as used manual stimulation) to induce lactation in myself. Plus my genetics were always more than a bit weird: I was more female than male even before I started HRT and surgical alterations...

Or in other words, my breasts (Tanner 5 with full lactation glandular development) are probably a bit different than most people reading this. So maybe my earlier comment about not seeing any significant breast reduction is not relevant. Particularly as I *do* eventually restart HRT after each of my hiatuses, so any resorption of glandular development that happens from going post menopausal tends to reverse itself. [I do typically notice the "ache" of breast growth/development for a while after I restart HRT again... which I have never really given much thought to, but is probably the just mentioned reversal of menopausal breast gland decreases...].

Which leads me to the last "partial true" note: The "actual duct tissue remains" thing. Sigh. When a woman goes menopausal, her glandular tissues deteriorate, with a gradual decrease in the amount of duct tissues in her breasts. That is a very slow process that takes years, though... and is only a *partial* resorption, not total, even after many years... but it does happen, although I have never experienced it as I always restart HRT before it becomes significant. Still, it is something to think about, if someone is contemplating stopping HRT indefinitely. Not only will fatty tissues be effected, but if it is kept up long enough even the glandular tissues may shrink... and the loss of skin and muscle elasticity does mean that the breasts will be more prone to sagging, too...

Shrug. Which should come as no surprise to anyone who has ever seen the breasts of an older (many years post menopausal) woman... which never really go away, but definitely do become smaller, droopy, and deflated. That is a process that takes many years, though.

If you want to stop HRT for a few months or so, Gwen, that is no big deal. Stopping it indefinitely... that is another story. When we sign up for SRS, we are also signing up for HRT for the rest of our lives. No one forces us to take those meds... but if we do not, there are consequences. Not just with the breasts, but with many parts of our bodies — especially the bones, the growth and repair of which are regulated by sex hormones...