Bulk transfer of fluid in the interstitial compartment of mammary tumors

Venous blood leaving a solid tumor showed higher erythrocyte concentration than did aortic blood. Net fluid loss of efferent blood as calculated from hematocrit differences was 2.7 to 6.7% of flow volume, 4.5 to 10.2% of perfusing plasma volume, or 0.14 to 0.22 ml fluid per hr per g in 2 to 5 g transplanted MTW9 and Walker 256 mammary carcinomas, and primary N-nitrosomethylurea- and 7,12-dimethylbenz(alpha)anthracene-induced mammary carcinomas of rats. Net fluid loss was directly related to blood flow but inversely related to tumor size. Increased hydrostatic pressure in tumor interstitial space was a consistent finding. Micropore chambers embedded in transplanted tumors drained 4 to 5 times more interstitial fluid than did identical chambers in the s.c. tissue. It is concluded that: (a) convective currents are present within the interstitial spaces of tumors; (b) the magnitude of fluid transfer can be measured by the difference in hemoconcentration between afferent and efferent tumor blood; and (c) the volume of this fluid transfer is not altered by hormone-induced tumor regression. The increased hydrostatic pressure of tumor interstitial spaces is interpreted as being due to absence of an anatomically well-developed lymphatic network. The bulk transfer of fluid within interstitial spaces is comparable to lymphatic drainage and should be considered in assessing drug concentration and distribution in solid tumors.