Cancer-related complaints filed with the Equal Employment Opportunity Commission have soared in recent years, growing faster than most charges.

By Vickie Elmer

FORTUNE -- Wal-Mart (WMT) paid $275,000 in a settlement after firing a long-time forklift driver after he had returned from cancer surgery. Home Depot (HD) paid $100,000 to settle a similar case where a 13-year employee was let go during treatments. A school social worker and a director of clinical services also were fired for cancer disability.

The number of cancer-related complaints filed with the Equal Employment Opportunity Commission has soared in recent years, growing faster than most charges. Cancer complaints, the initial report filed by a worker or ex-employee, rose 120% between fiscal years 2003 and 2013, when the number of complaints hit 974. ADA disability charges overall grew 72%, according to EEOC data.

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Part of the uptick has to do with the fact that Congress expanded what the Americans with Disabilities Act covers as of 2009.  Before that, there were questions over whether all kinds of cancers were covered, said Sharon Rennert, a senior attorney and advisor at the EEOC's Americans with Disabilities Act division.

Another reason for the gains: Employers are not training front-line supervisors on how they should manage a staff member with cancer or other serious diseases, said Rennert. They may not realize that as soon as the employee announces he has cancer, he's covered by the ADA's provisions and assistance.

"Every few years, you've probably got a new group of supervisors and managers. You need to repeat the training," she said. "Too often, employers draw a kind of black line," said Rennert. The manager has a knee-jerk reaction, assuming that once their 12 weeks of Family and Medical Leave Act unpaid time off are over, they must head back to work. "You've gotten your FMLA leave; you're done," is their thinking. In reality, "the ADA reasonable accommodation has to be assessed," she said.

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Reasonable accommodation is a squishy, undefined notion that varies based on the worker and employer's situations and resources. It could mean that the employee is eligible to do part-time work from home, or more frequent breaks, or a part-time schedule. Sometimes, an extra few weeks' leave (after the FMLA time is used up) would qualify as reasonable accommodation; other times, at a small company, it might be too much of a hardship on the coworkers and the company, Rennert said.

Employers are allowed to ask for medical documentation and need to "fill in an accurate picture of what's ahead" in a worker's cancer care.

Yet even medical centers don't get it right. Several health care and hospitals settled with the EEOC over discharging their own workers who were diagnosed cancer.