Are tumors more dense than surrounding tissue?
October 28, 2013 1:49 PM   Subscribe

If two people are the same height and physique, yet one weighs 20 lbs more than the other, could the difference be explained by one having a tumor?

This isn't something that I'm dealing with personally, just generally curious about the nature of tumors. I see stories about people having multiple pound tumors removed from their bodies without them knowing they were there, and wondering how that might happen.
posted by (bb|[^b]{2}) to Health & Fitness (9 answers total)
Tumors can be in areas where fat accumulates, so they can go unnoticed that way.
posted by Ruthless Bunny at 2:02 PM on October 28, 2013

Response by poster: But would they weigh more than the fat they displace?
posted by (bb|[^b]{2}) at 2:04 PM on October 28, 2013

Tumors are made out of all sorts of types of cells. Lipomas are fat cell tumors, so a lipoma probably wouldn't weigh any different than the fat it displaces. Teratomas can have all sorts of things in them, even bones and teeth.

How much a tumor would weigh relative to whatever it's sitting in would depend on the relative density of what actually makes up the specific tumor. So the answer to your question is, "yes, sometimes, but also sometimes no."
posted by phunniemee at 2:14 PM on October 28, 2013 [1 favorite]

It might not be a tumor. All my doctors tell me that I have "dense tissue", and when I tell people what I actually weigh, they're surprised. According to the doctors' charts I'm obese, but I'm clearly not.
posted by Melismata at 2:31 PM on October 28, 2013 [1 favorite]

Best answer: I think we can calculate whether this is even possible with cancerous tissue, based on the densities of various healthy tissues in the body.

Here is a cited table of body tissue densities.

Given the density values, one liter of muscle would have a weight of 1.06 kg and one liter of fat would have a weight of 0.9 kg.

20 lb is roughly equivalent to 9 kg.

1 L muscle = 2.3 lb
1 L fat = 2 lb

Let's say person A weighs 20 lb more than person B by replacing pure fat with pure muscle.

We keep A's volume the same as B's volume by removing 1 L of fat and replacing it with 1 L of muscle.

For every 1 L of fat subtracted from A, we add 1 L of muscle to A and gain 0.3 lbs.

We would therefore need to remove 66 L of fat and add 66 L of muscle to get a net addition of 20 lbs in weight, while preserving the same volume.

To put this in more human-sizable terms, 66 L is roughly 17 gallons, or 17 gallon-sized jugs of milk of new, pure muscle in A.

This seems unlikely.

If two people have the same outward appearance — that is, the same rough volume — and one person weighs 20 lbs more, then that person has something inside them that is very dense in comparison with fat, muscle — and even bone.

Let's say we replace 1L of fat in person A with 1L of pure bone:

1 L bone = 1.75 kg = 3.85 lbs
1 L fat = 2 lb

We again keep A's volume equal to B's volume by removing 1 L of something and replacing it with 1 L of something else.

For every 1 L of fat removed from A, we add 1 L of bone and gain 1.85 lbs.

For A to gain 20 lbs, therefore, we need to remove 10.8 L of fat and add 10.8 L of pure bone.

This is roughly 2.85 gallons (or three milk jugs) of bone we're adding to A, to gain 20 lbs.

This, too, seems unlikely.

I don't know the density of cancerous tissue, but looking at the numbers, that density value would need to be much higher than even bone for person A to have the same outward appearance of person B (i.e., same volume). This seems to be getting into density-of-lead (~11 g/cm3) territory to be plausible, and I don't think tumors can get anywhere near that dense.
posted by Blazecock Pileon at 2:41 PM on October 28, 2013 [3 favorites]

The other thing to consider is that there is a lot of squishy empty space in the body. Things like uterine fibroids often reach the size of grapefruits before they are detected! Same fibroids tend to be denser than fat, and probably can weight multiple pounds. I doubt that having 20 lb of tumours would be easy to distribute through the lower abdomen that easily to not see anything, but I would venture a guess that if they were just so, your intestines, bladder, liver etc would crowd upward and no visible external indicators would be possible.
If you're curious, search for fibroids... HUGE!
posted by Yavsy at 3:05 PM on October 28, 2013

For what its worth, an anecdote: my mother thought she was gaining weight, because her belly was getting bigger; however, her *actual* weight was pretty stable. When she finally bothered to go to a doctor about it, it turned out to be a 12-pound (benign) ovarian cyst --- about the size of a gallon of milk, but lighter in weight than other tissue.
posted by easily confused at 4:14 PM on October 28, 2013

More than likely a weight difference like that would be more explained by one person having more fat tissue in ratio to muscle than the other. Someone can be the same size but weigh more-they would have more muscle tissue. Five pounds of muscle takes up less space than five pounds of fat.
posted by St. Alia of the Bunnies at 4:41 PM on October 28, 2013

If two people are the same height and physique, yet one weighs 20 lbs more than the other, could the difference be explained by one having a tumor?

I'd be far more inclined to believe that the difference could be explained by inaccurate perception of the "same height and physique".

Consider two spherical humans of uniform density, weighing, say, 200lb and 220lb. Weight is proportional to volume, and volume is proportional to the cube (third power) of diameter. The ratio of the two weights is 1.1, so the ratio of the diameters is the cube root of that or roughly 1.03. Three percent is a pretty easy difference not to notice.
posted by flabdablet at 7:47 PM on October 28, 2013 [1 favorite]

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