An interesting project appeared briefly when I was approached Dr David Watmough and asked to help work out what might happen to a tumour mass when subjected to compression, as may happen during mammography. Could the practice of squeezing the breast tissue, to try to improve image quality, inadvertently result in disseminating cells with the potential of forming metastases? Some of the early literature (1-3) suggested that clinical examination and palpation ought to be done carefully to avoid dissemination of neoplastic cells and animal studies had shown that manipulation of tumours could increase the number of circulating neoplastic cells (4;5) , though others had questioned these findings (6) . We made some simple models and did some calculations to explore what might happen (7-9) .
During mammography, the breast is compressed between two plastic plates. Assuming that a tumour within the breast is initially spherical and that there is no change in volume during compression, it is possible to estimate the increase in surface area and in radial dimensions as it is compressed into the form of an oblate spheroid (9) (Figure 1). Figure 2 shows how, for a compression of 50% along one axis (applied strain), the surface area increases by nearly 25%. The orthogonal radial dimension, and hence the largest circumference, increases in length by 40% (radial strain). These strains are independent of the radius so will apply to any size of tumour.
Figure 1. An initially spherical object becomes oblate when compressed along one axis. If there is little or no change in volume then the orthogonal radius will increase, as will the surface area. |
Figure 2. Surface area and the radius orthogonal to the direction of compression increase as the sphere is compressed. |
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References
(1) Ide AG, Harvey RA, Warren SL. Role played by trauma in the dissemination of tumour fragments by the circulation. Arch Pathol 28 : 851-860, 1939.
(2) Quigley DT. Some negelected points in the pathology of breast cancer and treatment. Radiology : 383-386, 1928.
(3) Lyndham JEA. Pre and post operative treatment of the breast by radiation (metastasis excluded). Br J Radiol 4 : 534-560, 1931.
(4) Gazet JC. The detection of viable circulating cancer cells. Acta Cytol 10 : 119-125, 1966.
(5) Romsdahl MM, McGrath RG, Hoppe E, McGrew EA. Experimental model for the study of tumour cells in the blood. Acta Cytol 9 : 141-145, 1965.
(6) Fisher EA, Fisher B. Experimental study of factors influencing development of hepatic metastasesfrom circulating tumour cells. Acta Cytol 9 : 146-159, 1965.
(7) Watmough DJ, Quan KM, Aspden RM. Study of tissue compression in breast phantoms: possible implications for the use of X-ray mammography as a method for imaging breast carcinoma. European Journal of Surgical Oncology 18 : 538-544, 1992.
(8) Watmough DJ, Quan KM, Aspden RM. Unfavourable outcome of recent breast cancer screening trials: why? Am J Roentgenol 159 : 1125-1126, 1992.
(9) Watmough DJ, Quan KM, Aspden RM. Breast compression: a preliminary study. J Biomed Eng 15 : 121-126, 1993. |
